Download Detectable levels of interleukin-18 in uterine luminal secretions at

DOI: 10.1093/humrep/deh356
Human Reproduction Vol.19, No.9 pp. 1968–1973, 2004
Advance Access publication June 10, 2004
Detectable levels of interleukin-18 in uterine luminal
secretions at oocyte retrieval predict failure
of the embryo transfer
N.Lédée-Bataille1,2,4, F.Olivennes3, J.Kadoch3, S.Dubanchet1, N.Frydman3,
G.Chaouat1 and R.Frydman2
1
INSERM U131, Equipe Cytokines et Relation Materno-Fœtale Clamart, France, 2E.A 3538, qualité gamétique et implantation,
Clamart, France and 3Service de Gynécologie-Obstétrique et Médecine de la Reproduction, Hôpital Antoine Béclère, Clamart, France
4
To whom correspondence should be addressed at: Service de Gynécologie-Obstétrique, Centre Hospitalier de poissy, 10, Rue du
Champ Gaillard, 78300 Poissy, France. E-mail: [email protected]
BACKGROUND: Most implantation failures after successful in vitro fertilization-embryo transfer (IVF-ET) result
from inadequate uterine receptivity. There is currently no way to predict this receptivity. METHODS: We investigated whether the detection of interleukin-(IL)18 by ELISA in uterine luminal secretions might predict implantation failure. Secretions of 133 patients enrolled in our IVF-ET program were sampled by uterine flushing
immediately before oocyte retrieval. We assessed the following outcomes: pregnancy rate, multiple pregnancy rate,
and implantation rate per embryo transferred. RESULTS: Interleukin-18 was detected in the flushing fluid of
38 patients (28.6%). Although the two groups were comparable for all other characteristics (age, etiology, ovarian
reserve, number of embryos transferred, quality of embryos), all outcome variables differed significantly. The
pregnancy rate was 37.9% in the IL-18 2ve group and 15% in the IL-18 1 ve group, the multiple pregnancy rate
27.7% and 0%, and the implantation rate per embryo transferred 19.4% and 6.7% (all comparisons, P 5 0.02).
Only embryos meeting good quality criteria were transferred to 65 patients: 50 IL-18 2ve and 15 IL-18 1ve. The
pregnancy rate was 51% for the IL-18 2ve group and 20% for the IL-18 1ve group, the multiple pregnancy rate
36% and 0.0%, respectively, and the implantation rate 29% and 8.3% (P 5 0.02). CONCLUSION: This noninvasive and simple method predicted inadequate uterine receptivity, independent of embryo quality.
Key words: cytokines/implantation/interleukin-18/in vitro fertilization/embryo transfer (IVF-ET)/uterine flushing/uterine receptivity
Introduction
The implantation process, a complex and poorly understood
phenomenon, is currently the most critical problem in reproductive medicine, especially in assisted reproductive technology (ART). Only 15 to 20% of the embryos transferred after
in vitro fertilization (IVF) lead to the birth of a healthy baby
(ASRM/SART, 2002). When the quality of the embryo is
good, most implantation failures are imputable to inadequate
uterine receptivity (Smart et al., 1982; Simon et al., 1998)
and occur during the peri-implantation period (Racowsky,
2002). Progress in improving the rate of implantation
depends on a better understanding of the mechanisms underlying its success or failure.
Because of the low implantation rate after IVF and embryo
transfer (IVF-ET), multiple embryos are usually transferred
simultaneously to increase the likelihood of obtaining a pregnancy. This practice unfortunately also increases the rate of
multiple pregnancies. In 1998, the percentage of multiple
pregnancies reported after IVF-ET was 26.3% in Europe and
38% in North America (Toner, 2002). ART practitioners
1968
have long known that multiple pregnancies cause significant
maternal and especially fetal risk, in addition to their high
financial costs (Gardner et al., 2000; Gerris and Van Royen,
2000; Fanchin, 2001).
The study of uterine receptivity in humans relies primarily
on non-invasive methods such as ultrasound exploration, but
their predictive value and reproducibility are limited
(Fanchin, 2001). New methods are clearly needed to assess
uterine receptivity. Possible candidates include the measurement of various molecules involved in implantation, sampled
by uterine flushing or endometrial biopsy (Laird et al., 1997).
Mediators such as metalloproteases (Bischof, 2001), integrins
(Lessey et al., 1996) and cytokines (Delage et al., 1995;
Simon et al., 1995) have been successfully quantified with
these procedures. Cytokines are among the most important of
those mediators: implantation is controlled mainly, although
not exclusively, by locally acting growth factors and cytokines, some under steroid control (Giudice, 1994; Tabibzadeh
et al., 1995). The steroid hormones may initiate a downstream cascade of molecular events through local
Human Reproduction vol. 19 no. 9 q European Society of Human Reproduction and Embryology 2004; all rights reserved
IL-18 in uterine secretion predicts IVF failure
paracrine/autocrine molecules; these events include the intricate and entwined mechanisms of uterine receptivity and preimplantation embryo development.
IL-18 in vitro induces IFN-g and aberrant matrix metalloproteinase activity in the presence of IL-12. In its absence,
IL-18 causes the production of anti-inflammatory cytokines,
such as IL-4 and IL-13 (Smeltz et al., 2001; Abraham et al.,
2002). The administration of either IL-18 or IL-12 is abortifacient in mice (Kawamura et al., 1998; Hayakawa et al., 1999).
Thus, IL-18 induces both Th-1 and Th-2 cells, depending on
the local environment. Its pivotal role in the Th1/Th2 balance
(Lewkowich et al., 2002), its presence in the endometrium
(Yoshino et al., 2001) and its detrimental effects during pregnancy (Ida et al., 2000) suggested to us that its level in uterine
luminal secretions might function as an indicator of the cytokine environment.
Cytokines are not usually measured in uterine secretions
during cycles in which treatment procedures and IVF-ET
take place, for fear that direct access to the uterine cavity
might adversely affect the chance of pregnancy. Results are
thus extrapolated to other cycles, i.e. considered to remain
consistent. Because clear evidence shows that an individual’s
cycles vary in many ways, however, consistency cannot be
presumed. Once we had conducted a preliminary study to
confirm the safety of the procedure of uterine flushing performed at oocyte retrieval (i.e. during the treatment cycle,
48 h before embryo transfer) for implantation and pregnancy
rates (Olivennes et al., 2003), we were able to attempt to correlate the levels of some molecular mediators with the cycle
outcome. We used ELISA to assess the IL-18 concentration
in luminal uterine secretions at oocyte retrieval of 140
patients enrolled in our IVF program. At the same time, we
measured the IL-18 concentration in follicular fluid (pooling
the fluid for all follicles for each woman) for 50 of them.
The study outcomes were the rates of pregnancy and implantation following those IVF-ET cycles.
Methods
Patients
Between July 2001 and July 2002, 140 patients enrolled in our IVF
program underwent a uterine flushing during the same procedure as,
but immediately before, oocyte retrieval. The choice of patients,
while not random, was essentially arbitrary: it depended on whether
two specific physicians (F.O., J.K.) were performing the procedure.
We included only patients with controlled ovarian hyperstimulation
before the IVF procedure. All patients enrolled in the program had
previously undergone hysteroscopy and ultrasound assessment of
their uterine cavity to measure its size and assess any particularities.
Patients with tumors, a septate uterus, or any other uterine malformations were excluded.
All patients provided informed consent, and our Institutional Review Board approved this investigation (CCPPRB, protocol 01 – 78).
Protocol for the controlled ovarian hyperstimulation
Most patients (71.4%, n ¼ 100) received a standard gonadotrophinreleasing hormone agonist (GnRH-ag) regimen, beginning on day
21 of a spontaneous menstrual cycle. Leuprolide acetate (1 mg
per day, Lucrin, Takeda Pharmaceuticals, Paris, France) was
administered subcutaneously for 10 – 14 days, until complete suppression of pituitary activity. The remaining 40 patients (21.8%)
received a GnRH antagonist (Cetrotide, Serono, France) during
stimulation, without prior pituitary desensitization. Stimulation
began once serum oestradiol was , 50 pg/ml and sonographic evidence indicated no follicular activity and an endometrial lining
,5 mm thick. Recombinant (rFSH: Puregon, Organon Pharmaceuticals, Saint Denis, France or Gonal F, Serono, France) or purified
urinary gonadotrophin (FSH-LH: Menopur, Ferring, France) treatment then began, at a daily dose of 225 IU, subcutaneous. The duration of these doses depended on the standard criterion of follicular
maturation, assessed by both ultrasound and serum oestradiol
measurements. HCG (‘endo’ chorionic gonadotrophin; Organon
Pharmaceuticals, Saint Denis, France, 10000 IU, intramuscular) was
administered when at least three follicles were mature (. 17 mm in
diameter) and the estrogen level per mature follicle was
.250 pg/ml. Thirty-six hours after HCG administration, the uterine
flushing was performed as described below and oocytes were
retrieved by needle aspiration, with transvaginal ultrasound guidance
under intravenous sedation or local anesthesia. All patients received
antifungus pessaries (Gynomyk, Labo, France, two doses vaginally)
the day before and the morning of oocyte retrieval and an intravenous bolus of antibiotics (amoxicillin and clavulanic acid, Augmentin, Adventis, France, 1 g) during the procedure. For 50 women, we
also kept a sample of follicular fluid, pooled from all the follicles
used. The uterine flushing and follicular fluids were stored separately at 2 208C in mini-vials until IL-18 measurement by ELISA.
All patients received the same treatment after oocyte retrieval:
micronized progesterone (Utrogestan; Besins-Iscovesco Pharmaceuticals, Paris, France) (400 mg daily, vaginally) and ciprofloxacin
(Ciflox, Adventis, France) (1000 mg daily for 5 days).
Embryo quality was evaluated according to the regularity of the
blastomere and the percentage of fragmentation (Veeck, 1990). The
blastomeres in grades A and B were even, with no fragmentation in
grade A and , 20% in grade B. Both were defined as good-quality
embryos. Grade C had either uneven blastomeres or . 20% fragmentation, and grade D . 50%. Of 140 patients who underwent
uterine flushing, 133 had an embryo transfer on day 2 or 3.
Uterine flushing
The uterine flushing took place just before the oocyte retrieval and
before intravenous sedation or local anesthesia. All information
about difficulties in accessing the uterus were recorded, so that the
flushing also served as a dry run for the embryo transfer 48 h later.
The in vivo method for uterine flushing is neither painful nor
invasive. As we have described previously, we gently insert an
embryo transfer catheter (Frydman catheter, CCD Laboratories,
Paris, France), connected to a 10 ml syringe. We then instill 1 ml of
saline water, immediately and gently aspirate it, and repeat these
two steps. The low quantity and lack of viscosity of the saline water
instilled minimizes leakage (Ledee-Bataille et al., 2002; Olivennes
et al., 2003).
The liquid was then stored for 140 patients at 2 208C in minivials until the assays. Flushing samples were discarded before storage in 15% of the cases because either its fluid volume was too
small (, 200 ml) or it contained mucus.
Cytokine assays
Il-18 concentrations in uterine flushing and follicular fluids were
assayed by enzyme-linked immunosorbent assay (ELISA) according
to the manufacturer’s instructions (Quantitine Human IL-18 ELISA
kit, R&D, ref no. 7620). This test had a sensitivity limit of
12.5 pg/ml. Intra-assay coefficients of variation were 4.45, 3.55
1969
N.Lédée-Bataille et al.
Table I. Clinical patients’ characteristics
Group
IL-18 2ve
n ¼ 100 (%)
Mean [IL-18]
pg/ml
IL-18 þ ve
n ¼ 40 (%)
Mean [IL-18]
pg/ml
No. of patients and mean [IL-18] (pg/ml)
Age
Parity Nulliparity Primiparity
100
33 ^ 0.4
90 (90%)
10 (10%)
0
40
32 ^ 0.6
47 (92%)
3 (8%)
63 ^ 10
Etiology
Male factors
Permanent tubal factors
Partial tubal factors
Endometriosis
Unexplained infertility
Preimplantation diagnosis
No. of previous attempts
FSH on Day 3 (mIU/ml)
E2 on Day 3 (pg/ml)
48 (48%)
16 (16%)
9 (9%)
5 (5%)
14 (14%)
8 (8%)
2 ^ 0.3
6 ^ 2 0.2
36 ^ 3
0
0
0
0
0
0
0
0
17 (45%)
4 (10%)
4 (10%)
5 (12.5%)
5 (12.5%)
4 (10%)
2 ^ 0.1
6 ^ 0.3
26 ^ 3
60 ^ 15
48 ^ 10
66 ^ 16
41 ^ 7
78 ^ 28
39 ^ 10
86 ^ 30
23 ^ 7
140 patients underwent in vitro fertilization. The clinical characteristics of patients with detectable IL-18 in their uterine
flushing fluid (IL-18 þ ve: 40 patients) were compared with those without (IL-18 2ve: 100 patients). The details of the
respective etiology in each group is described with the correspondent mean and standard error of IL-18 in each group.
The two groups were comparable for all the indicators we examined. We did not observed statistical differences
in function of the etiology.
and 4.59%, respectively, for IL-18 at concentrations of 80, 400 and
1000 pg/ml and Inter-assay coefficients of 4.26, 3.42 and 1.02%.
For calculating purposes, samples with a concentration below that
limit were assumed to contain 0 pg/ml of IL-18.
Statistical analysis
The results were expressed as the mean ^ standard error. All variables for the IL-18 þve and IL-18 2 ve groups were compared with
a standard Student’s t-test, run under StatView software (Abacus
Concepts, Inc., Berkeley, CA). Clinical pregnancy was defined by
ultrasound identification of at least one gestational sac with cardiac
activity; it did not include biochemical pregnancy. The pregnancy
rate was defined as the ratio of the number of clinical pregnancies
to the number of transfers, and the implantation rate, the ratio of the
number of gestational sacs to the number of embryos transferred. A
P-value of 0.05 or less was considered significant.
Results
IL-18 was detected in the flushing fluid of 40 of the 140
samples tested (28.57%) (IL-18 þ ve group). The mean IL-18
concentration in this group was 63.42 ^ 10 pg/ml (14 – 330).
The IL-18 þ ve group did not differ significantly from the
IL-18 2 ve group for any other variables except outcomes.
Their clinical profiles (age, ovarian reserve, parity, number
of IVF attempts, causes of sterility) were non significantly
different and are detailed in Table I. However, among
patients with detectable IL-18, the higher concentrations of
IL-18 were described for patients with idiopathic and partial
tubal sterility (none had hydrosalpinx diagnosed at the ultrasound evaluation). In contrast, the lowest concentrations
were traced in those fertile patients who were enrolled in
IVF for preimplantation diagnosis. However, the observed
differences were not significant.
The protocols used for the controlled ovarian hyperstimulation, the respective hormonal and biological responses in
the IL-18 þ ve and 2 ve groups are detailed in Table II. In
patients with IL-18 detectable, the concentration of IL-18
was not significantly higher in those patients who received an
1970
antagonist protocol than in patients who received GnRH agonist (P ¼ 0.77).
IL-18 þ ve and 2 ve groups did not differ for the number
of oocytes collected, the number of embryos produced, or the
number of embryos transferred. Even the quality of the
embryos was the same. Embryos were transferred into 95 of
the 100 IL-18 2 ve patients and 38 of the 40 IL-18 þ ve
patients.
The outcome, however, differed dramatically according to
whether IL-18 was detectable (Table III). The clinical pregnancy rate was 16% in the IL-18 þ ve group and 38% in the
IL-18 2 ve group (P ¼ 0.02), and the implantation rates were
6.7% and 19% respectively (P ¼ 0.02).
As expected, embryo quality also affected pregnancy rates
significantly: they were best (47.75%) among the 65 patients
with only good-quality embryos (grade A or B) transferred,
and intermediate (34%) among the 40 patients with mixed
embryos transferred (AB þ CD). No pregnancies occurred
among the 35 patients who had only low-quality embryos
(grade C or D).
Of the 65 patients who had only good quality embryos
transferred, 15 were IL-18 þ ve and 50 IL-18 2 ve. In this
subgroup, for which embryo quality was controlled, the
implantation rate also differed dramatically according to
IL-18 status: 8.3% in the IL-18 þ ve group compared with
29% in the IL-18 2 ve group (P ¼ 0.02). The multiple pregnancy rates were respectively 0% and 36% (P ¼ 0.03).
The sensitivity of the detection of IL-18 to not predict
further pregnancy or multiple pregnancy is high: 85% and
100%, respectively. But the specificity of the detection of
IL-18 for the pregnancy and multiple pregnancy rate is low
(no detection of IL-18 does not predict pregnancy): 35% and
34%, respectively. The detection of IL-18 has a high negative
predictive value for further pregnancy but a poor positive
predictive value.
The mean concentration of Il-18 in the follicular fluid
from 51 samples was 240 ^ 96 pg/ml. However only six
IL-18 in uterine secretion predicts IVF failure
Table II. Characteristics of the ovarian hyperstimulation
Group
Protocol
GnRH Agonist protocol
GnRH antagonist
E2 Day HCG (pg/ml)
Endometrial thickness (mm)
No. of oocytes collected
No. of embryos of quality A þ B transferred
No. of embryos of quality C þ D transferred
No. of embryos transferred
No. of patients with transfers
IL-18 2ve
[IL-18]
pg/ml
IL-18 þve
[IL-18]
pg/ml
74 (74%)
26 (26%)
2808 ^ 182
9 ^ 0.35
10 ^ 0.7
2 ^ 0.2
1.1 ^ 0.2
2.6 ^ 0.1
95
0
0
26 (65%)
14 (35%)
2444 ^ 109
9 ^ 0.1
9 ^ 0.5
2 ^ 0.1
0.9 ^ 0.24
2.6 ^ 0.1
38
73 ^ 16
49 ^ 9
P-value
(t-test)
0.71
0.89
0.46
0.56
0.24
0.8
140 patients underwent in vitro fertilization. The characteristics of the ovarian stimulation (protocol, concentration of IL-18, ovarian response) of patients with
detectable IL-18 in their uterine flushing fluid (IL-18 þ ve: 40 patients) were compared with those without (IL-18 2ve: 100 patients). The repartition for the
agonist and antagonist protocols in each group is detailed with the correspondent mean and standard error of IL-18. The two groups were comparable for all the
indicators we examined. Neither was there a statistical difference in the protocol used (P ¼ 0.29).
Table III. Outcome
Group
All patients transferred (n = 133)
IL-18 2ve
95
IL-18 þ ve
38
P-value
Implantation Rate
Pregnancy rate
Multiple pregnancy Rate
Transfer of only embryos
A þ B (n = 65)
Implantation Rate
Pregnancy rate
Multiple Pregnancy rate
Transfer of only embryos
C þ D (n ¼ 35)
Implantation Rate
Pregnancy rate
19.4%
37.8%
27.7%
50
6.7%
15.7%
0%
15
0.02
0.02
0.04
0.02
29%
51%
36%
26
8.3%
20%
0%
9
0.04
0.03
0%
0%
0%
0%
NS
NS
NS
Implantation Rate (IR), Pregnancy Rate (PR) and Multiple Pregnancy Rate
(MPR) are reported for patients in the IL-18 þ ve and 2ve groups. IR is
calculated independently of embryo quality, when only embryos of quality
A þ B were transferred and when only embryos of quality C þ D were
transferred.
patients with detectable uterine luminal IL-18 were evaluated
for their follicular fluid IL-18 concentration versus 45 in the
group with no luminal IL-18 detectable. We thus could not
conclude if IL-18 concentration in follicular fluid differed
according to whether the patient’s uterine flushing contained
IL-18. The concentration of IL-18 however in the uterine
flushing fluid was not significantly correlated with that in the
follicular fluid for the six patients observed. Follicular fluid
concentration was not correlated to the basal FSH level, the
number of oocytes collected, the embryos number or quality
and the implantation rate.
Discussion
The detection of IL-18 in the uterine lumen, i.e. at the time
of oocyte retrieval, 48 h before embryo transfer, is associated
with a poor implantation rate. To understand this finding, we
must consider here the implications of the presence of this
cytokine.
We begin by assuming that the IL-18 detected in the flushing liquid is of local origin, i.e. secreted by the uterus. IL-18
is synthesized as a 24 kDa molecule that requires cleavage by
IL-1 converting enzyme (ICE, also known as caspase-1) to
generate a biologically active 18 kDa monomer (Ghayur
et al., 1997; Gu et al., 1997). These functions are mediated
through the IL-18 receptor (IL-18R), which is identical in
sequence to a member of the IL-1 receptor family previously
designated IL-1 receptor-related protein (Torigoe et al.,
1997). A constitutively secreted and soluble binding protein
for IL-18 was recently purified from human urine (IL-18 BP)
(Novick et al., 1999). It neutralizes IL-18 effector functions
(Novick et al., 1999). Yoshino et al. (2001) report that the
complete system is present in the human endometrium. In
contrast to other pro-inflammatory cytokines, which are
expressed cycle-dependently and usually peak in the luteal
phase, expression of the IL-18 family (IL-18, IL-18R,
IL-18BP) shows no characteristic variations during the menstrual cycle (Yoshino et al., 2001).
Expression of the IL-18 protein appears to occur mainly
in endometrial epithelial cells, almost entirely as its 24 kDa
precursor protein, which is biologically inactive and is not
secreted unless it undergoes cleavage (Yoshino et al., 2001).
Nonetheless, the mature IL-18 protein may be secreted by
some human epithelial cells in situations such as Chlamydia
trachomatis infection (Lu et al., 2000). Because the percentage of tubal sterility was equal (23%) in the Il-18 þ ve and
IL-18 2 ve groups in our series, this factor is not exclusive
to explain the differences observed. However, the high
IL-18 concentrations observed in some patients in the partial
tubal and unexplained infertility groups, suggest that these
patients should be tested for existence of a latent Chlamydia
infection and then, if positive, accordingly treated. However,
the five patients with unexplained infertility and a high
IL-18 luminal concentration were negative for C. trachomatis. This suggests that this etiology is not exclusive and that
some underlying uterine dysregulation should also be
searched for.
Detection of Il-18 in the uterine lumen suggests that
local factors not yet defined induce the transformation of
pro-IL-18 into mature IL-18 and then modify the local
environment. We thus hypothesize that detectable level of
IL-18 in the uterus reveals a pre-implantation stage-specific
1971
N.Lédée-Bataille et al.
defect in the implantation process that results in improper
uterine preparation and thus inadequate receptivity during the
implantation window.
IL-18 was initially described as an interferon (IFN)-g inducing factor in human that acts in synergy with IL-12 to
enhance the cytotoxic activity of human natural killer (NK)
cells and promote T-helper 1 (Th-1) response by production
of TNF and IFNg (Nakamura et al., 1989; Matikainen et al.,
2001). In mice, high NK activity (cytostatic or cytotoxic),
high levels of LFN-g or TNF and low levels of such Th-2
cytokines as IL-10 are known to be abortifacient (Chaouat
et al., 1995).
Studies on animal model also shown that IL-18 was able
limit the induction of type 2 immunity in vivo (Lewkowich
et al., 2002) and leads to aberrant matrix metalloproteinase
(MMP) activity with IL-12 (Abraham et al., 2002).
We can therefore hypothesize that detectable IL-18 in the
uterus at the time of oocyte retrieval indicates cytotoxic NK
cell activity, accompanied by dysregulation of both type 2
immunity and MMP activity; both of these are associated
with implantation failure (Lin et al., 1993; Wegmann et al.,
1993; Chaouat et al., 1995).
This outline, attractive as it seems, may nonetheless be too
simplistic in view of the complexity of the IL-18 system
(Hoshino et al., 2001). Indeed, IL-18 has been demonstrated
to be positively involved in the implantation process in
mice (Ostojic et al., 2003) and human (Lédée-Bataille et al.,
in press). Furthermore, vascular remodeling of the spiral
arteries appears to require IL-18 activity to stimulate NK
cells to produce angiopoietin-2 (Croy et al., 2000, 2003). The
effects of Il-18 are highly dependent on the presence (and
absence) of other cytokines (amongst which IL-12 and IL-4
have been most studied). The presence, quantity and ratio of
these cytokines determine whether IL-18 shifts the immune
system towards differentiation of Th-2 cells or promotes
Th-1 cell proliferation (Smeltz et al., 2001). IL-18 BP
(mostly expressed in endometrial stromal cells) can also
decrease IL-18 activity by reducing IFN-g-mediated
responses (Reznikov et al., 2000). A complete interpretation
of our results therefore requires further documentation of
other cytokines, including IL-12 and IL-18BP (an IL-18
antagonist), by simultaneous human endometrial biopsy. The
expression of the cytokines in the uterine luminal compartment does not reflect the evolving complexity of the endometrial cytokine network itself but is a selection of one type
of expression/secretion in a specific phase of the cycle.
As for leukaemia inhibitory factor (LIF), intrauterine
secretion of these cytokines, by the uterine epithelium in
the pre-implantation period, may not reflect the situation in
the peri-implantation/immediate post-implantation period,
in the endometrium itself, especially right around spiral
arteries (Ledee-Bataille et al., 2002).
Regardless of the underlying pathology, however, excess
luminal IL-18 constitutes for the clinician an immunological
marker that can predict implantation failure with a significant
degree of accuracy (strong negative predictive value and
specificity) and is detectable relatively rapidly by a noninvasive method before embryo transfer. Furthermore, this
1972
marker is predictive independently of embryo status, another
factor that strongly affects implantation rates. Its detection
should invite the clinician in case of failure to further uterine
exploration especially in context of unexplained sterility or
partial tubal sterility in order to enhance the uterine
receptivity.
As is the case for most of the markers of uterine receptivity, detection of IL-18 has a poor positive predictive value
and sensitivity since others factors as the embryo quality will
interact to predict the pregnancy. The absence of detection of
IL-18 should therefore be associated with these others prognosis parameters to evaluate the risk of multiple pregnancy.
Today, most policies to reduce the percentage of multiple
pregnancies either select the best embryo to transfer by predefined criteria (the TOP embryo), (Gerris et al., 2000) or by
in vitro culture until the blastocyst stage (Gardner et al.,
2000; Schoolcraft et al., 2001). Combining this approach of
embryo selection with assessment of the local cytokine
environment in the uterine cavity could theoretically improve
our transfer strategies: we might either reduce the number of
embryos transferred if they are of good quality and IL-18 is
not detected (high risk of multiple pregnancy) or choose
either to freeze them or to replace up to three embryos if
IL-18 is detected and the embryos quality non optimal (low
risk of multiple pregnancy).
In the near future, we will understand the full significance
and origin of this IL-18 dysregulation and be able to propose
adequate molecular corrections.
Acknowledgements
We thank Jo Ann Cahn for revising the manuscript. This work
was supported by INSERM and the Fondation de la Recherche
Médicale.
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Submitted on March 10, 2003; accepted on May 14, 2004
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