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E European Society of Human Reproduction and Embryology
Human Reproduction Update 1999, Vol. 5, No.4 pp. 373–385
Hypothesis on the role of sub-clinical bacteria
of the endometrium (bacteria endometrialis) in
gynaecological and obstetric enigmas
D.A.Viniker
Department of Obstetrics and Gynaecology, Whipps Cross Hospital, London, UK
Unexplained infertility, recurrent abortion, dysfunctional uterine bleeding, pelvic pain, premenstrual syndrome,
premature labour, placental insufficiency and pre-eclampsia are examples of common obstetric and gynaecological
problems that frequently defy adequate explanation. Bacterial vaginosis, a non-inflammatory condition, is associated with
premature labour, but antibiotics administered topically provide less effective prophylaxis than those administered orally.
This would indicate that bacterial vaginosis might be a marker for significant genital tract bacteria, but some pathology is
dependent on micro-organisms ascending out of reach of topical antibiotics. The author was led to consider the hypothesis
that micro-organisms, possibly those associated with bacterial vaginosis, surreptitiously inhabit the uterine cavity (bacteria
endometrialis) where they are culprits of some common gynaecological and obstetric enigmas. The objective of this review
is to provide an initial theoretical examination of this hypothesis. Bacteria in the endometrium have been associated with
infertility. Antiphospholipids have been linked to recurrent miscarriage and pre-eclampsia and with infections including
Mycoplasma. Pre-eclampsia might be explained by an exaggerated host response to intrauterine micro-organisms or
bacterial toxins. The hypothesis that one common factor, bacteria endometrialis, could provide a plausible explanation for
a variety of obstetric and gynaecological mysteries is particularly intriguing. There is sufficient evidence to justify further
investigation.
Key words: endometrial bacteria/pre-eclampsia/recurrent miscarriage/subclinical bacterial infections/unexplained infertility
TABLE OF CONTENTS
Introduction
Bacterial vaginosis
A comparison of bacterial vaginosis and bacteria
endometrialis
Dysfunctional uterine bleeding and pelvic pain
Bacteria endometrialis and unexplained infertility
Pregnancy complications and sub-clinical bacteria
of the endometrium
Conclusions
Acknowledgements
References
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certainly, each of these clinical syndromes has more than one
initiating pathological process, which confound scientific
analysis. At a recent conference, ‘The Problem with
Prematurity II’, held at St Thomas’ Hospital, London, 7–9th
September 1998, a variety of thought-provoking papers was
presented. On reflection, several of these papers led the author
to the above hypothesis. It is becoming apparent that
micro-organisms associated with bacterial vaginosis (BV) are
capable of initiating local symptoms without clinical evidence
of inflammation, as well as a pathological process as potentially
devastating as prematurity. Expanding knowledge about BV
may enhance our ability to consider the possible implications of
BV-type organisms higher up the genital tract.
Introduction
Numerous hypotheses have been expounded to explain a
number of obstetric and gynaecological syndromes: invariably,
they may meet some—but not all—of the criteria. Almost
Bacterial vaginosis
More than a century ago, Alfred Doderlein (1892) discovered
that lactobacilli are inhabitants of the vagina, where they have a
Address for correspondence: Department of Obstetrics and Gynaecology, Whipps Cross Hospital, Whipps Cross Road, Leytonstone, London E11 1NR, UK
374
D.A.Viniker
symbiotic relationship with their host. The vaginal flora is
normally dominated by lactobacilli, which are responsible for
reducing the pH by metabolizing glycogen from squamous
cells to lactic acid. The resultant acidic milieu provides
protection against infection.
BV is recognized as the most common cause of vaginal
discharge and it was once believed to be no more than a nuisance
that could be ignored in asymptomatic women. The discharge
tends to be malodorous, particularly after intercourse. A
remarkable feature of BV is the absence of a host reaction; thus,
the suffix ‘osis’ rather than ‘itis’ is preferred because signs of
inflammation are usually absent (Hay, 1994; Donders, 1998).
A variety of organisms can be cultured from the vagina in
asymptomatic, as well as symptomatic, women. Bacteriological observations on vaginal samples are therefore more
difficult to interpret than those obtained from sites where
sterility would be expected. In the 1950s, the investigation and
management of vaginal discharge was revolutionized (Gardner
and Dukes, 1955) when the organism now called Gardnerella
vaginalis was first described. BV has become the adopted term
to describe a clinical condition characterized by an overgrowth
of predominantly anaerobic bacteria within the vagina and a
concomitant reduction or absence of lactobacilli.
A change in pH, possibly following menstruation or sexual
intercourse, may be the trigger for BV to develop. Women with
BV are found to have a group of micro-organisms present in high
concentrations. This group includes the anaerobic organisms
G.vaginalis, Mobiluncus, Bacteroides, Peptostreptococcus
species and Mycoplasma hominis and Ureaplasma urealyticum.
There are a number of strains of some of these micro-organisms
(Grattard et al., 1995). Mycoplasmas are the smallest free-living
micro-organisms, with a high incidence of antigenic variation
and variable reactivity to monoclonal antibodies (Christiansen
et al., 1997). Some BV organisms are described as being
opportunistic. The clinical manifestations of BV may depend on
a synergistic interaction of a variety of these organisms (Levett,
1989). It is unknown whether there is one particular microbe that
is responsible for BV, or even whether the principal organisms
are among those previously cited or are still to be identified (Hill,
1993).
The diagnosis of BV can be made by the presence of three
out of four of the following: a homogeneous discharge; pH
>4.7; positive amine test; and ‘clue’ cell identification (Amsel
et al., 1983; McGregor and French, 1998). The laboratory
investigation for BV is dependent on microscopy (Donders,
1998) rather than culture. A Gram stain of vaginal fluid may
assist diagnosis (Spiegel et al., 1983).
The incidence of BV is increased in underprivileged
communities. G.vaginalis can be recovered from the urethrae
of male sexual partners (Gardner and Dukes, 1955). BV is
mostly related to sexual activity, although it has been
demonstrated in virgins (Bump and Buesching, 1988).
Organisms associated with BV can be transmitted from mother
to neonate (Dinsmoor et al., 1989; Gannon, 1993). The mode
of transmission of BV organisms remains controversial. Recent
studies (Holst, 1990) suggested that BV organisms may
colonize the vagina from the woman’s intestinal tract. It is now
considered that although BV is usually sexually transmitted,
this is not exclusively the case (MacDermott, 1995).
The Gram-negative organisms, including Bacteroides, are
sensitive to the antibiotic metronidazole, whereas Mycoplasma,
Ureaplasma and Mobiluncus are sensitive to macrolide
antibiotics such as erythromycin, and to the tetracyclines.
A comparison of bacterial vaginosis and
bacteria endometrialis
The bacteriological investigation of the vagina and
endometrium are compared in Table I. This shows how the
possible significance of bacteria endometrialis (BE) could have
been missed or overlooked.
Table I. A comparison of the bacteriology of the vagina and
endometrium, showing how the possible significance of bacteria
endometrialis could have been missed or overlooked
Vagina
Endometrium
Rich in micro-organisms
Relatively sterile.
High vaginal swabs: routine
clinical investigation
Samples confined to research
centres.
Bacterial vaginosis: diagnosis by
microscopy of wet preparation or
Gram stain
Wet preparations and Gram
stain: not studied
Culture unhelpful for bacterial
vaginosis
Culture only. Specialist centres
required for Mycoplasma
hominis and Ureaplasma
urealyticum
Possible marker for bacteria
endometrialis
Micro-organisms can be present
even with negative cervical
cultures
Bacterial vaginosis: no clinical
inflammation (‘-osis’, not an ‘-itis’)
Micro-organisms can occur with
negative clinical examination
High vaginal swabs are frequently obtained in routine clinical
practice, whereas the bacteriology of endometrial samples has
been studied only by a few research groups. Many
micro-organisms can colonize the vagina without being
pathogenic. The bacteriological diagnosis of BV is dependent on
microscopic assessment of a wet preparation of the discharge or a
Gram stain rather than culture, whereas investigation of the
endometrium has depended on culture alone.
Despite extensive investigation, the significance of the varied
patterns of bacteria found in the vagina remains controversial
(Donders, 1998). Our knowledge about endometrial organisms is
comparatively spartan and more difficult to interpret. There is an
association between cervical colonization with U.urealyticum
and chronic endometritis (Khatamee and Sommers, 1989).
Micro-organisms can be present in the endometrium when
cervical cultures are negative (Lucisano et al., 1992).
Subsequently, endometrial microbiology and histopathology
Sub-clinical bacteria of the endometrium
were evaluated in women with symptomatic bacterial vaginosis
but no clinical evidence of pelvic inflammatory disease (Korn
et al., 1995). Plasma cell endometritis was found in 10 of the 22
women studied compared with one of the 19 controls (P < 0.01).
Positive endometrial cultures for BV-associated organisms were
significantly more common in association with plasma cell
endometritis (P = 0.002), but eight of 30 women without
histological changes also had positive cultures. It may be that BV
is a marker for BE, but there is probably a poor correlation
(Koren and Spigland, 1978). Bacteria have been identified in the
endometrium in asymptomatic as well as symptomatic women
(Table II).
Dysfunctional uterine bleeding and pelvic pain
Menorrhagia is a frequent gynaecological problem that can be
debilitating. The term dysfunctional uterine bleeding is adopted
when no clinically obvious causation can be found (Viniker,
1997a). Pelvic inflammatory disease is recognized as a cause of
menstrual disturbance, although in clinical practice the
diagnosis is usually dependent on evidence of salpingitis. The
significance of chronic endometritis remains an area of debate.
Some claim that even a few plasma cells in the endometrium
375
are diagnostic, but these cells may be found in healthy women
(Fox, 1973a). It was concluded (Tindall, 1987) that it is illogical
to apply the term to those with menorrhagia or pelvic pain.
Pathogenic micro-organisms have been demonstrated in the
endometrium without evidence of pelvic infection being
visible at laparoscopy and with negative cervical cultures
(Lucisano et al., 1992). An interesting hypothesis has been put
forward (Profet, 1993) that menstruation is designed to flush
out intrauterine infection: increased menstrual flow is a sign
that the uterus has detected infection. In a double-blind study,
metronidazole tablets (500 mg) or a placebo were administered
daily to 42 gynaecological outpatients with irregular bleeding
or discharge and BV (Larsson et al., 1990). Mobiluncus sp. was
identified in 81% of cases before treatment. Metronidazole
gave a cure rate of 76% compared with 5% in the placebo
group; repeated therapy, when required, achieved a cure rate of
100%. It was concluded that it is important to treat BV in
patients with symptoms other than malodorous discharge. The
bacteriology of the endometrial cavity was evaluated
immediately after hysterectomy in 99 women (Moller et al.,
1995), with nearly a quarter of the endometria being shown to
be colonized by one or more microorganism.
Table II. Clinical studies of the bacteriology of the cervix/vagina and endometrial cavity
Reference
Clinical situation
Organism
Cervix/vagina
N1
Idriss et al. (1978)
Koren and Spigland (1978)
Stray-Pedersen et al. (1982)
Kundsin et al. (1986)
Naessens (1987)
Cararach et al. (1998)
Normal
Infertility
-Unexplained
-Explained
Normal
Infertile
Normal
Infertile
Infertile
Normal pregnancy
Induced abortion
Normal fertile
Spontaneous abortion
Recurrent abortion
Uncontrollable
Preterm labour
Normal
U.urealyticum
Mycoplasma
U.urealyticum
Mycoplasma/
Ureaplasma
U.urealyticum
Culture (all relevant
organisms)
Preterm labour
Normal
Preterm labour
Normal
Preterm labour
Normal
Preterm labour
Mycoplasma
Gram-negative
Bacteria
Gram stain
67
161
40
121
50
59
40
379
99
310
84
41
122
76
6
4
30
22
59
58
30
59
30
59
29
59
N2
22
72
22
50
Intrauterine site
%
47
57
Endometrium
Endometrium
129
35
17
65
49
5
%
3
16
3
98
64
6
27
7.5
26
65
33
45
55
41
Endometrium
19
215
N3
41.6
41.6
41.5
53.3a
64.5a
83
8
27
24
41
7
16
0
8
1
13
23
27
0
13.6a
3.4
22a
Endometrium
9.7%
9.7
Endometrium
Placenta
Amniotic fluid
27.6%
4
2
27.5
66
50
Amniotic fluid
2
2
N1 = no. of patients studied; N2 = no. of patients with positive culture at cervical/vaginal site; N3 = no. of patients with positive culture at
intrauterine site.
aP < 0.05.
376
D.A.Viniker
Figure 1. Histology of endometrium from a 36-year-old lady with
intermenstrual bleeding. This was initially assessed to be a possible
focus of adenocarcinoma, but subsequently confirmed as focal intraendometrial abscess with regenerative atypia. Original magnification ×40. Scale bar = 20 µm.
A 36-year-old lady was admitted for diagnostic laparoscopy
to investigate pelvic pain. As there had been some recent
intermenstrual bleeding, hysteroscopy, cervical dilatation and
endometrial curettage were also performed. The histological
assessment of the curettings initially indicated a possible focus
of well-differentiated adenocarcinoma, but on reassessment the
lesion proved to be focal intra-endometrial abscess with
regenerative atypia (Figure 1). In another study, the
characteristic subacute inflammation of the endometrium was
described (Kundsin et al., 1986) and believed to be associated
with Mycoplasma infection.
The significance of endometriosis in relationship to pelvic
pain is debated. Some women with extensive disease are
asymptomatic, whereas others with minimal disease report
severe pain. An endometriosis session held during ESHRE’s
7th Annual Meeting in 1991 concluded that “Endometriosis
does not exist; all women have endometriosis” (Evers, 1994).
Recent studies have shown that the symptoms of endometriosis
are related to local inflammation (Taylor et al., 1997).
It is possible that there may be micro-organisms in the pelvis
that are causing symptoms without evidence of inflammation.
Recently, we have been prescribing metronidazole and
erythromycin around the time of laparoscopy, even in the
absence of positive findings. Results have been encouraging,
but larger patient numbers and controlled studies would be
required before validated conclusions could be made.
Bacteria endometrialis and unexplained
infertility
Infertility is a common problem that affects 15% of couples.
Only half of these will eventually have a child (Templeton,
1995). Anovulation, pathology of the Fallopian tubes and male
factor problems may be found in about 75% of couples
investigated for infertility (Viniker, 1997b). Depending on the
criteria employed, infertility remains unexplained in about
25% of cases. Ovulatory disorders can be successfully treated
with simple orally administered ovulation-stimulation
regimens (Viniker, 1996). Audit provides a means of
improving the quality of care provided in fertility programmes
(Viniker, 1999). Reviews of the literature have not given high
priority to the concept that unexplained infertility might be due
to sub-clinical intrauterine infection (Viniker, 1997b).
Similarly, there has been little attention to the potential
contribution of antibiotics for unexplained infertility (Viniker,
1997c).
The role of infection as a cause of infertility is well
recognized, but this is almost exclusively in relation to the
Fallopian tubes. Cytokines secreted by endometrial leukocytes,
which could be associated with infection, have been implicated
in reproductive failure (Rutanen, 1993).
A variety of micro-organisms in the endometrium have been
associated with infertility (Emembolu, 1989). Important
pathogens, such as Chlamydia trachomatis, can be present in
the upper genital tract without evidence of pelvic infection
being visible at laparoscopy and with negative cervical cultures
(Lucisano et al., 1992). Several groups have concluded that
C.trachomatis might be a cause of unexplained infertility in
otherwise asymptomatic couples (Bjercke and Purvis, 1992;
Berclaz et al., 1993; Greendale et al., 1993; Xiang and Chen,
1996). In contrast, no difference was found in the incidence of
seropositive patients in infertile and fertile couples (Auroux
et al., 1987).
It was considered (Czernobilsky, 1978) that endometrial
biopsy was an essential tool in the evaluation of infertility, the
conclusion being that endometritis plays a significant role in the
aetiology of subfertility. Plasma cells, which are evidence of
chronic infection, and foci of lymphocytes in the endometrium
may be the sole clue of Mycoplasma endometritis (Jones and
Jones, 1981). Mycoplasma may be implicated in some cases of
unexplained infertility, but a positive culture is difficult to
obtain as the technique requires expertise (Kundsin et al.,
1986). Endometrial washings taken from 59 women with
unexplained infertility showed 16 patients (27%) to prove
positive for Mycoplasma, and five (31%) of these conceived
within a few months of a 7-day course of the antibiotic,
doxycycline (Koren and Spigland, 1978). These authors
concluded that endometritis due to Mycoplasma could be a
cause of infertility. A further investigation was conducted in
161 consecutive infertility patients and 67 controls for
U.urealyticum (Idriss et al., 1978). Of the patients with
unexplained infertility, 55% had a positive culture from the
endocervix compared with 32% of the controls (P = 0.03). In
another study, Mycoplasma was isolated from 18% of infertile
women, though patients with evidence of Mycoplasma in the
endometrium had no specific histological feature (Bercovici
et al., 1978).
Sub-clinical bacteria of the endometrium
A series of 379 women with infertility were examined for the
presence of U.urealyticum and the results were compared with
those from 40 controls (Stray-Pedersen et al., 1982). The
organism was demonstrated in the cervix in about half of each
group. There was a significant increase (P < 0.05) in positive
cultures from the endometrium in the infertile group (26%)
compared with the controls (7.5%) which could not be related
to tubal pathology or male infertility; neither could results be
attributed to contamination during sampling.
In a study of 100 consecutive infertile middle and
upper-class infertile couples with longstanding failure to
conceive and who were previously under the care of others
(Kundsin et al., 1986), genital Mycoplasma was cultured from
64 of the women, and antibodies to Chlamydia were present
in 23. Endometrial histology showed evidence of Mycoplasma
in 47 of the 86 patients biopsied, while 24 of the 39 negative
biopsies yielded Mycoplasma on culture.
Antibiotics for uterine bacteria in infertility
Antibiotic therapy for infertility associated with infection
specifically of the endometrium or cervix has received
relatively scant attention. A search of the literature located no
reference to sub-clinical infection as possible causation of
infertility. Cervical infection has been implicated as a cause of
infertility, and doxycycline was found to be efficient at
reducing cervical mucus infection (Buvat et al., 1984).
Following treatment there were nine pregnancies within four
months in a group of 13 women with otherwise unexplained
infertility of more than a year.
A probable beneficial effect was found for couples with one
partner having doxycycline for proven Mycoplasma infection
(Hinton et al., 1979), but this could not be confirmed
(Upadhyaya et al., 1983).
In another study, tetracycline (500 mg, four times daily) was
administered to both partners for 2 weeks if the endocervical
culture of Mycoplasma taken at the time of postcoital test
proved positive (Idriss et al., 1978). In the six months
following treatment, the pregnancy rate was 42% compared
with 32% without treatment, although this was not statistically
significant. Others (Kundsin et al., 1986) administered
oxytetracycline, if there was evidence of Mycoplasma, to their
patients and partners for 10 days. If endometrial cultures were
positive on repeat sampling 3 months later, a more prolonged
and higher dose regimen was provided. There were 43
pregnancies among 58 patients (71%) who had been followed
for one year after treatment.
Seminal infection and infertility
There has been only one reported study evaluating
metronidazole in relation to semen quality (Gopalkrishnan
et al., 1990). This group examined the semen from 1131
asymptomatic men, 50 of whom were found to have
Trichomonas, and these were treated with metronidazole (400
377
mg, three times daily) for 10 days. Significant improvement in
semen quality was demonstrated in 25 cases, the authors
concluding that some cases of infertility in asymptomatic men
could be due to Trichomonas, though they do not seem to have
considered that the antibiotic might have been inadvertently
treating other organisms.
There is evidence that spermatozoa are vectors of disease
(Profet, 1993) as, during mammalian insemination, bacteria
from the male and female genital tract cling to sperm tails and
are transported to the uterus. Indeed, an affinity of human
spermatozoa for U.urealyticum has been demonstrated
(Nunez-Calonge et al., 1998).
Reactive oxygen species, which are produced by leukocytes,
have an adverse effect on sperm function and are frequently
observed in the semen of infertile men. Reactive oxygen
species are frequently encountered with infections in general,
and specifically in association with male accessory gland
infection (Depuydt et al., 1996; Wang et al., 1997).
Antioxidant treatment, however, probably provides little
benefit (Martin-Du Pan and Sakkas, 1998). A Medline search
of the literature found no evaluation of the possible benefit of
erythromycin or metronidazole in relation to reactive oxygen
species. The clinical significance of sub-clinical infection in the
semen remains controversial (Eggert-Kruse et al., 1995).
Pregnancy complications and sub-clinical
bacteria of the endometrium
Recurrent abortion and bacteria endometrialis
Spontaneous abortion is estimated to occur in approximately
20% of pregnancies (Salat-Baroux, 1988). A standardized
definition for recurrent abortion has not been universally
adopted, but many apply the term to three consecutive
miscarriages. Recurrent abortion affects between 0.4 and 0.8%
of couples. A variety of factors have been implicated, including
maternal congenital Mullerian anomalies, fibroids, intrauterine
adhesions, cervical incompetence, fetal genetic disorders,
elevated maternal luteinizing hormone (LH) concentrations,
antiphospholipid syndrome, general maternal medical
disorders, toxins and psychological disorders. The role of
infectious agents remains to be elucidated (Carp, 1997). The
one study that has investigated the possible relationship
between BV and recurrent miscarriage (Llahi-Camp et al.,
1996) demonstrated an increased incidence of BV with
second-trimester miscarriage rather than first-trimester loss.
The role of intrauterine colonization with organisms such as
Mycoplasma has been difficult to evaluate (Salat-Baroux,
1988). U.urealyticum was found in the cervix of 41.6% of 310
normal pregnant women, in 53.3% of 122 women with
spontaneous abortion, and in 64.5% of 76 women with
recurrent spontaneous abortion (Naessens et al., 1987). The
isolation of this organism was significantly higher in
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D.A.Viniker
association with spontaneous abortion (P < 0.05) and recurrent
abortion (P < 0.005). In these studies, endometrial colonization
by U.urealyticum was found to be more common in women
with recurrent abortion (27.6%) than in normal fertile women
(9.7%; P < 0.05).
On administering doxycycline or erythromycin to women
with recurrent abortion and genital Mycoplasma, the
pregnancy loss rate was diminished with both antibiotics,
although better results were recorded with erythromycin
(Quinn et al., 1983). The course of subsequent pregnancies
following doxycycline therapy after primary or recurrent
spontaneous abortions in 254 couples was investigated (Toth
et al., 1986), and the outcome found to be significantly better in
the antibiotic-treated group, while the rate of spontaneous
abortion recurrence was significantly lower (10% versus 38%).
The incidence of premature rupture of the membranes was
reduced after antibiotics (4% versus 30%), and there were
significantly lower neonatal complications after antibiotics
including prematurity, fetal distress, meconium, respiratory
distress syndrome and neonatal infection. These authors
concluded that spontaneous abortion might be caused by
bacteria present in the genital tract at the time of conception.
These bacteria might have an adverse effect on the course of
pregnancy and result in increased maternal and fetal
complications.
A Medline search of the literature revealed no reference to
the use of metronidazole as a treatment for recurrent
miscarriage.
Pregnancy complications and the
antiphospholipid syndrome
In a series of 933 consecutively booked pregnant women, 20
women (2%) had lupus anticoagulant or anticardiolipin
(Pattison et al., 1993). These conditions were found in 15% of
women with recurrent miscarriage (Rai et al., 1995). Seven
women among a group of 43 (16%) presenting with severe
pre-eclampsia before 34 weeks gestation had antiphospholipid
antibodies (Branch et al., 1989). Women with positive results
are at increased risk for recurrent pregnancy loss, intrauterine
growth retardation, pre-eclampsia, placental abruption,
perinatal morbidity and mortality (Pattison et al., 1993;
Lakasing and Poston, 1997). The mechanism underlying these
adverse outcomes has yet to be described (Lakasing and
Poston, 1997). It is not known whether the antiphospholipids
are a direct cause of these pregnancy complications, or an
epiphenomenon (Rai and Regan, 1998). In the context of the
hypothesis that micro-organisms within the uterus may be
associated with pregnancy complications, it is intriguing that
there is an association between a variety of infections,
including Mycoplasma, and antiphospholipid antibodies
(Snowden et al., 1990; Catteau et al., 1995).
The most rewarding cause of recurrent abortion from the
treatment point of view is the presence of lupus anticoagulant
and anticardiolipin. Aspirin, heparin, steroids and
immunoglobulins have been evaluated (Rai and Regan, 1998).
Clinical trials have confirmed significant benefits with aspirin
and combined aspirin and low-dose heparin. Antibiotics do not
seem to have been considered.
Some in-vitro fertilization (IVF) units, including our own,
administer antibiotics at the time of egg collection to reduce the
risk of pelvic infection, though it is possible that this would be
treating undiagnosed BV or BE. We have commented
previously on our low miscarriage rates, which we were unable
to explain (Viniker et al., 1997). A national study has been
commenced to compare outcomes between IVF units
according to their antibiotic policy.
Premature labour
Premature delivery and placental insufficiency, with
accompanying fetal oxygen deprivation (Viniker, 1979), are
the leading causes of perinatal mortality and morbidity.
Premature birth can be due to the culmination of a variety of
interdependent factors, one of which is cervical length
(Newman, 1998). Epidemiological trends in the prevalence of
prematurity are difficult to interpret, as there are a number of
confounding factors. Risk factors for premature delivery
include previous low birth weight, maternal illness (including
diabetes) and vaginal infections (Di Renzo et al., 1998).
There is increasing evidence that BV is related to premature
labour (Hauth et al., 1995; Di Renzo et al., 1998; McGregor
and French, 1998). The vaginal fluid of pregnant women with
BV has higher concentrations of mucolytic enzymes, including
mucinases and sialidases (McGregor et al., 1994). It was
suggested that these enzymes could adversely affect host
defences during pregnancy, increasing the risk of sub-clinical
intrauterine infection and premature delivery. In addition to
premature labour, an association has been found with fetal
growth retardation and stillbirth (Lamont et al., 1998). As a
result of their investigations, these authors suggest that
screening and treating for BV in pregnancy is likely to prove
advantageous. Erythromycin and metronidazole can reduce the
prevalence of premature delivery in women with bacterial
vaginosis (Hauth et al., 1995). Treatment with topical vaginal
antibiotics has proved less effective for prevention of
premature delivery than oral antibiotics (Majeroni, 1998;
McGregor, 1998). This would indicate that the
micro-organisms responsible for premature labour have
ascended out of reach of topically administered antibiotics.
Warnings have been expressed (Brocklehurst, 1999) that trials
of treatment to prevent premature delivery need to demonstrate
a benefit for the baby; until this has been confirmed, such
treatment should be seen as experimental.
We have reviewed the records of 413 women with BV
attending the Department of Sexual Health at Whipps Cross
Hospital from 1994 (D.Viniker, K.Ihuoma and R.Melville,
unpublished results). In total, 382 women were symptomatic
Sub-clinical bacteria of the endometrium
and were treated with metronidazole alone or in combination
with tetracycline or with clindamycin; 31 were asymptomatic
and not treated. Twenty-four of the women have attended our
obstetric department. Twelve had treatment for BV before or
during pregnancy and these all had uneventful outcomes, and
12 were found to have BV after pregnancy. One woman had a
spontaneous abortion at 14 weeks gestation and two women
had premature deliveries; nine had favourable outcomes. We
believe that there is a tendency to cross district borders to attend
departments of genitourinary medicine, so that our dataset is
unlikely to be complete.
The amniotic cavity should be sterile. Evidence linking
intrauterine infection with long-term morbidity, including
cerebral palsy, has been reviewed (Romero, 1998). Microorganisms were found in the fluid retrieved by amniocentesis in
25% of all premature births and in 10% of cases of premature
labour with intact membranes, and there was also evidence of a
role for proinflammatory cytokines in the onset of human
labour.
The frequency of sub-clinical intra-amniotic infection and
cervical bacterial colonization in relation to preterm labour has
been evaluated (Cararach et al., 1998). These authors looked at
two cohorts—59 women with preterm labour and 30 controls
who had amniocentesis to assess fetal lung maturity. There was
a statistically increased incidence of Gram-negative vaginal
bacteria in patients with premature labour, but no increase in
intra-amniotic infection. A group of six women with
uncontrollable preterm labour and intact membranes resulting
in fetal loss between 20 and 28 weeks gestation were also
investigated (Naessens et al., 1987). Intra-amniotic
U.urealyticum was detected in only two women, the organism
being isolated from the cervix in five cases and from the
placenta in four. It would seem, therefore, that if U.urealyticum
has a part in premature labour, it would be active extraamniotically rather than intra-amniotically.
It has been suggested (Corfield et al., 1998) that the
susceptibility of the cervical mucus to bacterial degradation
may be a factor in premature delivery, and evidence was found
of increased enzyme activity in patients with BV. The
identification of genitourinary infections, most notably BV, can
consistently reduce premature delivery and premature rupture
of the membranes (McGregor and French, 1998). The
recommended prophylactic treatment has been oral
clindamycin or metronidazole.
A relationship has been observed (Chen et al., 1996)
between miscarriage and premature delivery; this would be
predictable if BV is a cause for both such complications of
pregnancy.
Pre-eclampsia and bacteria endometrialis
Pre-eclampsia is a complication of pregnancy characterized by
hypertension, proteinuria and fluid retention. It may develop at
an alarming speed with attendant risks of maternal mortality
379
and morbidity (Hunter et al., 1998). The causation of
pre-eclampsia remains a mystery, and it seems probable that
more than one factor is responsible. A summary of facts
associated with pre-eclampsia and eclampsia that must be met
by a hypothesis are summarized in Table III. With reference to
Table III, if micro-organisms within the uterine cavity play a
part in the aetiology of pre-eclampsia then it is possible that a
state of immunization occurs to the dominant organism. This
could explain the association with first pregnancy [Table
III(A)]. Micro-organisms may be carried into the female
genital tract attached to spermatozoa (Nunez-Calonge et al.,
1998). A different strain of organism could be acquired from a
new partner, resulting in a subsequent increased risk of
pre-eclampsia [Table III(B)].
Table III. Facts associated with pre-eclampsia
A. Occurs preferentially during first pregnancies
B. Change of partner alters the incidence for later pregnancies
C. Placental structural changes by early second trimester
D. Increased incidence with hydatidiform mole
E. Clinical presentation in late second trimester or in the third
trimester
F. Placental tissue required
G. Extrauterine pathology including renal, hepatic and coagulation
H. Increased incidence in multiple pregnancy and diabetes
I. Familial tendency
J. Ethnic variation
It has been suggested (Toth et al., 1986; McGregor, 1998)
that there might be endometrial infection at the time of
implantation. The presence of micro-organisms within the
uterine cavity could explain abnormal placentation [Table
III(C)]. The uterus is full of trophoblastic tissue when there is a
hydatidiform mole [Table III(D)]. There may be a complex
relationship between the competence of the cervix and
ascending genital tract infection (Jones et al., 1998). In early
pregnancy the cervix is closed, providing a degree of protection
against micro-organisms ascending. As term approaches, the
cervix shortens and opens so that this mechanical protection is
lost and more organisms could easily gain entrance into the
uterine cavity [Table III(E)]. The micro-organisms would be
removed when the uterus is completely emptied of placenta and
membranes following delivery [Table III(F)]. In multiple
pregnancy, the membranes and placental volume are larger and
the cervix may shorten and start to dilate earlier [Table III(H)].
The placenta tends to be larger in diabetic pregnancy [Table
III(H)]. BV can occur in virgins, and the organisms are known
to be passed from mother to neonate, possibly contributing to
familial tendency [Table III(I)]. Finally, women of black race
have an increased incidence of BV during pregnancy
(Goldenberg et al., 1996) and also pre-eclampsia (Knuist et al.,
1998) [Table III (J)].
380
D.A.Viniker
Current theories on the pathogenesis of pre-eclampsia relate
to changes in the renin–angiotensin–aldosterone system (Carr
and Gant, 1983; Morgan et al., 1997), immunological
susceptibility (Jenkins et al., 1978; Redman et al., 1978),
disseminated intravascular coagulopathy (Roberts et al.,
1989), prostacyclin and thromboxane (McParland et al., 1990)
and maternal endothelial cell damage (Roberts et al., 1989).
Each of these theories, however, relates to susceptibility or
perpetuation of the syndrome rather than the triggering
mechanism.
According to one theory (Roberts et al., 1989), poorly
perfused placental tissue releases one or more factors into the
systemic circulation. This results in endothelial cell damage
and a subsequent cascade of disseminated intravascular
coagulation, vasoconstriction and body fluid redistribution.
Endothelial cell dysfunction, which is a characteristic of the
maternal syndrome of pre-eclampsia, might be caused by a
factor released from the placenta into the maternal circulation.
A fluoroimmunoassay has been developed (Knight et al.,
1998) to measure syncytiotrophoblast microvilli (STBM) in
the blood of pregnant women. These authors found that STBM
are released into the circulation in greater amounts in
pre-eclampsia than in normal controls. The concentrations of
STBM in plasma correlated with endothelial anti-proliferative
activity, indicating that STBM in the circulation may be
involved in the endothelial dysfunction seen in pre-eclampsia.
Monocytes were shown to phagocytose STBM, and this could
possibly be linked to the release of cytokines and other toxins,
which would enhance endothelial damage. There seems to be
an already well-developed inflammatory response in normal
pregnancy, so that the differences between normal pregnancy
and pre-eclampsia are less apparent than those between normal
pregnancy and the non-pregnant state. From these
observations, it was concluded (Redman et al., 1998) that
pre-eclampsia arises from a universal maternal intravascular
inflammatory response to pregnancy, and there is then an
additional stimulus or the maternal response is unduly strong.
The current view is that endothelial cell dysfunction is a
common end-point for a variety of causes of pre-eclampsia.
Pre-eclampsia is associated with dyslipidaemia and
overproduction of free radicals, which is reminiscent of
atherosclerosis (Hubel, 1998). There is a change in placental
morphology by 20 weeks gestation in patients likely to develop
pre-eclampsia. There are restricted endovascular trophoblast
invasion and atherotic lesions with local trophoblast
destruction. An imbalance of maternal inflammatory cells and
cytokine production may lead to the release of toxic factors and
cytokines from the placenta, resulting in the clinical syndrome
of pre-eclampsia (Pijnenborg, 1998). Early identification of a
change in placental blood flow might provide a useful
screening test for the subsequent development of
pre-eclampsia (Campbell et al., 1986).
Many screening tests have been developed, but lack of
uniformity in the definition of pre-eclampsia confounds the
analyses (Poulton et al., 1998). Hyperuricaemia and
thrombocytopenia, as well as liver enzymes, provide a measure
of some clinical value (Shennan, 1998), and ultrasound
Doppler screening looks reasonably promising (Campbell,
1998). Vascular endothelial growth factor (VEGF), a protein
released by damaged endothelium, is elevated in women with
pre-eclampsia. Preliminary data have shown elevated levels of
VEGF as early as 12 weeks gestation in women destined to
develop pre-eclampsia, and there is a more than 3-fold increase
by 20 weeks. This would suggest that VEGF may prove to be a
useful screening test for pre-eclampsia (Hunter et al., 1998). It
has been predicted (Redman et al., 1998) that there is no single
gene disorder, single specific predictive test, nor a single
preventive effective measure, though optimism has been
expressed that the future of pregnancy screening will focus on
ultrasound (Campbell, 1998); pregnant women will have an
early dating scan, early mid-trimester anomaly scan, and
Doppler ultrasound at 24 weeks to predict high risk for
pre-eclampsia.
There would appear to be a familial predisposition to
pre-eclampsia and eclampsia, which is presumed to be genetic
(Hubel, 1998). It is recognized that pre-eclampsia is a complex
disorder reflecting the interaction of genes and ‘environmental’
factors (O’Shaughnessy, 1998). If there is an association
between bacterial vaginosis and premature labour, as well as
with pre-eclampsia, then there should be an increased
incidence of premature labour with pre-eclampsia. This point
has been confirmed (Chen et al., 1996), and it was also found
that preterm births were almost twice as likely to occur in
women with pregnancy-induced hypertension and more than
four times more likely to occur in women with
pregnancy-aggravated
hypertension
compared
with
normotensive women (Samadi and Mayberry, 1998).
Possible modes of bacterial action in pre-eclampsia
Chorioamnionitis is a term applied loosely to leukocyte
infiltration of the placenta and extraplacental membranes. A
high incidence of chorioamnionitis is found in cases of
pre-eclamptic toxaemia, but this has been attributed to
prolonged rupture of the membranes in these cases (Fox,
1973b). The most compelling argument to refute the
hypothesis of BV-type organisms being a factor in
pre-eclampsia is the poor correlation with chorioamnionitis. If
intrauterine infection with BV-type organisms is the elusive
‘Scarlet Pimpernel’, then it could have been masked by the fact
that evidence of an inflammatory response has not been
forthcoming. To reiterate, BV is an ‘-osis’ rather than an ‘-itis’.
How could bacteria endometrialis be responsible for the
typical clinical features of pre-eclampsia and eclampsia? Two
contending mechanisms would be exaggerated host response
and bacterial toxins.
Reproductive function, cytokines and exaggerated host response: Cytokines are potent polypeptides released from in-
Sub-clinical bacteria of the endometrium
flammatory cells as part of the host response. They have
multiple paracrine and endocrine functions, and there are complex mechanisms for control and cessation of their actions
(Galley and Webster, 1996). Cytokines have a central, but potentially, paradoxical role in the immunological and inflammatory processes. They are part of the local defence mechanism
against infectious disease, but they are also implicated as
mediators of the pathology of infectious disease (Henderson
et al., 1996). The body contains an enormous number of microorganisms, which constitute the normal microflora; indeed, it
has been estimated that there is a greater number of bacteria in
the body than cells. Bacteria and viruses may produce molecules that induce inflammatory and anti-inflammatory reactions in the host.
Endometrial receptors for cytokines have been demonstrated
(Tabibzadeh, 1991). There is increasing evidence that
cytokines, in addition to their role in the immune system, may
have a significant role in the modulation of the neuroendocrine
control of reproduction (Rutanen, 1993; Mathialagen and
Roberts, 1994). Cytokines probably play a physiological part
as local mediators of the actions of sex hormones on the
endometrium (Tabibzadeh and Sun, 1992; Sharkey, 1998).
Leukocyte numbers and cytokine expression are altered in
some women with implantation defects (Stewart-Akers et al.,
1998). Cytokines released by activated endometrial
lymphocytes and macrophages can have a detrimental effect on
embryo implantation and embryo development (Shaarawy and
Nagui, 1997).
A variety of conditions, not initially related to infection, can
produce a state of shock that is indistinguishable from aspects
of septic shock. It is, therefore, apparent that it is the host
response to the severe insult, which is responsible rather than
the initiating stimulus. This host response has become known
as the systemic inflammatory response (SIRS) (Beal and Cerra,
1994). The immuno-inflammatory cascade can be initiated by
toxins from micro-organisms. The main mediators of SIRS are
the cytokines, particularly the interleukins (IL)-1 and IL-6 and
tumour necrosis factor-α (TNFα). During the early stages of
infection, the cytokines play an essential homeostatic role and
their activities are mainly localized, with only minimal
systemic effects. The inter-relationships between cytokines are
complex. They may act synergistically so that their combined
effects may be different from their individual actions
(Offenstadt et al., 1993). Occasionally, there may be failure of
cytokine control, leading to SIRS; when cytokine control has
been lost, SIRS becomes self-sustaining with multiple organ
dysfunction (Bone, 1991) [Table III (G)].
Toxins: The once popular concept of circulating toxin as the
cause of hypertension and proteinuria in pregnancy fell into
disrepute, apparently for lack of supportive evidence (Carey,
1974). The vaginal fluid of women with bacterial vaginosis
contains significantly greater amounts of endotoxin than in
controls (Sjoberg and Hakansson, 1991; Mattsby-Baltzer et al.,
1998). BV-associated endotoxins are capable of inducing cyto-
381
kine production in pregnancy (Mattsby-Baltzer et al., 1998).
An animal model for pre-eclampsia has been described (Faas
et al., 1994) which involves ultra-low-dose endotoxin infusion
in conscious, pregnant rats. The endotoxin, or saline for the
controls, was infused for 1 h on the 14th day of gestation, and
blood pressure, albuminuria and platelet counts were
measured. A significant increase was found in blood pressure
and albuminuria in the index group, while platelet coagulopathy and glomerular fibrinogen deposits were observed only
in the endotoxin-treated group. The authors concluded that
their model resembled the clinical and histopathological events
of pre-eclampsia sufficiently to enable further investigation
into the pathophysiological mechanisms of the condition.
Subsequent studies have confirmed that pregnancy greatly influences the nature and strength of the inflammatory response
following endotoxin administration (Faas et al., 1995). The
results of infusing ultra-low-dose endotoxin into non-pregnant
rats was also described (Faas, 1998). There was no effect with
the first infusion, but if it was repeated 18–24 h later, a state
typical of pre-eclampsia developed. When the endotoxin was
administered to pregnant rats on just one occasion, the preeclampsia changes were seen.
It was also suggested (Henderson et al., 1996) that
understanding the control mechanisms of cytokine release
induced by micro-organisms will advance anti-inflammatory
therapy. If bacteria within the uterus are responsible for
pre-eclampsia, there could be a role for antibiotics in the
prophylaxis and treatment of this potentially lethal syndrome.
A search of the literature using Medline has revealed no
reference to the use of metronidazole or erythromycin in the
prevention or management of pre-eclampsia.
Conclusions
In recent years, an unexpected infectious aetiology has been
found for a variety of clinical conditions. In gynaecology, the
role of the human papillomavirus in pre-malignant and
malignant cervical disease has been confirmed and in
obstetrics, we are learning of the relationship between BV and
premature delivery, while Helicobacter pylori has become
established as the cause of peptic ulceration. There is also a
body of evidence implicating microbes in the pathogenesis of
coronary heart disease, and although the bacteria Chlamydia
pneumoniae (Jackson et al., 1997; Maass et al., 1998) and
H.pylori appear to be the leading contenders, a number of
viruses have also been suggested (Ellis, 1997). If bacteria in the
endometrial cavity should be implicated as a significant,
previously unrecognized, cause of obstetric and
gynaecological disease, the place of appropriate antibiotic
regimens would need careful consideration. Clinical trials
involving pregnant women are not common. It is never easy to
explain the concept of risk to patients, and this is compounded
by the presence of an unborn child (Mohanna, 1998). The
agents of choice for bacterial vaginosis are metronidazole for
382
D.A.Viniker
the anaerobes, and erythromycin for Mycoplasma.
Erythromycin is also effective against C.trachomatis.
Pharmaceutical companies advise that metronidazole should
only be given with caution during pregnancy, although several
groups have reassuringly demonstrated no evidence of
teratogenicity (Morgan, 1978; Roe, 1983; Piper et al., 1993;
Burtin et al., 1995; Czeizel and Rockenbauer, 1998).
Nevertheless, a policy of caution—particularly in the first
trimester—and avoidance of high-dose regimens in pregnancy
would seem appropriate.
How can the clinical significance of BE be evaluated? We
need to consider the classical principles of Koch, to review
retrospectively appropriate databases, and to contemplate
serological studies and perhaps trials of therapy.
According to Koch’s principles, the micro-organism must:
(i) be found in all cases of the disease; (ii) be isolated from the
host and grown in pure culture; (iii) reproduce the original
disease when introduced into a susceptible host; and (iv) be
found in the experimental host so infected.
The variety of organisms possibly implicated in ‘bacteria
endometrialis’, the number of clinical conditions that could
result, and their nature, are such that it is difficult to foresee how
these principles could be tested. There is evidence that
micro-organisms often contaminate the uterine cavity of some
healthy women, although they are found more frequently in
association with pathological processes. Bacteriological
diagnosis of BV is not assisted by culture, and it is possible that
this would also pertain for BE. Facilities to culture
Mycoplasma are limited to a few centres.
Developments in serological tests are enhancing our
capability to detect evidence of infections in gynaecology.
C.trachomatis heat shock proteins have been related to
infertility (Witkin et al., 1998) and ectopic pregnancy (Sziller
et al., 1998). Serological tests for Mycoplasma pneumoniae are
used in current clinical practice, but not for M.hominis or
U.urealyticum. Some research workers have started to evaluate
new serological tests for U.urealyticum (Quinn et al., 1993),
M.hominis (Shimada et al., 1998) and Mobiluncus (Schwebke
et al., 1996).
Finally, there is the option for a trial of therapy for patients
with a presumptive diagnosis without laboratory confirmation.
The antibiotics of choice—metronidazole and the macrolides
such as erythromycin—are relatively innocuous. Nevertheless,
antibiotics should be used with caution, as there are risks of
bacterial resistance. In a study of induced abortion, women
allocated to receive antibiotics had lower infection rates than
those allocated to treatment only if screening was positive
(Penney et al., 1998). With approval by our Ethics Advisory
Committee, we have commenced a controlled study of
erythromycin and metronidazole for all couples presenting
with infertility and/or recurrent abortion.
The hypothesis that one common factor, bacteria
endometrialis, might provide a plausible explanation for a
variety of obstetric and gynaecological enigmas is particularly
intriguing. There is sufficient evidence to warrant further
investigation.
“We seek him here, we seek him there,
Those Frenches seek him everywhere.
Is he in heaven? – Is he in hell?
That demmed, elusive Pimpernel”.
The Scarlet Pimpernel, Baroness Orczy (1905)
Acknowledgements
Several colleagues have kindly provided invaluable advice. For
their kindness and wise counsel, the author wishes to thank Mr
R.Baldwin, Mr P.Breen (Latin teacher), Dr B.Chattopadhyay,
Mrs A.Clemenson, Dr C.Jain, Mr R.Lamont, Professor
J.MacVicar, Dr R.Melville, Mr E.E.Philipp, Professor
L.Poston, Professor C.Rodeck, Professor S.K.Smith, Professor
C.W.G.Redman, Mr G.Sadler, Professor P.Steer, Dr K.Thomas
and Professor H.Youssef.
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Received on December 12, 1998; accepted on April 20, 1999