Download Phases and duration of the second stage

CHAPTER 17
Physiology and care during the
transition and second stage
phases of labour
Dr. Areefa Albahri
The chapter aim s to
consider the nature of the transition and second stage
phases of labour
describe the usual sequence of events during these
stages
summarize signs of transition and of the expulsive
phase of labour
discuss the care of the mother, father and birth
companions
review the observations that should be carried out at
this time
discuss the physiology of birth and the role of the
midwife when the term fetus is presenting by the
breech.
The nature of the transition and second stage phases of labour
The second stage is the phase between full dilatation of the cervical os, and the
birth of the baby.
Most midwives and labouring women are aware of a transitional period between
the period of cervical dilatation, and the time when active maternal pushing
efforts begin.
This is typically characterized by maternal restlessness, discomfort, desire for
pain relief, a sense that the process is never-ending, and demands ' to end the
whole process.
Uterine action
Contractions become stronger and longer but may be
less frequent, allowing both mother and fetus regular
recovery periods.
The membranes often rupture spontaneously
towards the end of the first stage or during transition
to the second stage.
Fetal axis pressure increases flexion of the
presenting part, resulting in smaller presenting
diameters, more rapid progress and less trauma to
both mother and fetus. If the mother is upright during
this time, these processes are optimized.
Soft tissue displacement
As the fetal head descends, the soft tissues of the pelvis
become displaced. Anteriorly, the bladder is pushed
upwards into the abdomen where it is at less risk of injury
during fetal descent. The fetal head becomes visible at the
vulva, advancing with each contraction and receding
between contractions until crowning takes place. The head
is then born. The shoulders and body follow with the next
contraction, accompanied by a gush of amniotic fluid and
sometimes of blood. The second stage culminates in the
birth of the baby.
Recognition of the commencement of the second stage of labour
A. Presumptive evidence
1. Expulsive uterine contractions
Some women feel a strong desire to push before full dilatation occurs.
Traditionally, it has been assumed that an early urge to push will lead to
maternal exhaustion and/or cervical o-edema or trauma.
More recent research indicates that the early pushing urge may in fact be
experienced by a significant minority of women, and that, in certain
circumstances, spontaneous early pushing may be physiological.
It is not clear whether these findings are influenced by factors such as
maternal or fetal position, or parity, and there is not enough evidence to
date to determine the optimum response to the early pushing urge.
2. Rupture of the fore waters
Rupture may occur at any time during labour.
3. Dilatation and gaping of the anus
Deep engagement of the presenting part may produce this
sign during the later part of the first stage.
4. Anal cleft line
Some midwives have reported observing this line (also called
‘the purple line’) as a pigmented mark in the cleft of the
buttocks which gradually ascends the anal as the labour
progresses.
5. Appearance of the rhomboid of Michaelis
It presents as a dome-shaped curve in the lower
back, and is held to indicate the posterior
displacement of the sacrum and coccyx as the
fetal occiput moves into the maternal sacral
6. Upper abdominal pressure & epidural analgesia
7. Show
This is the loss of bloodstained mucus which often
accompanies rapid dilatation of the cervical os
towards the end of the first stage of labour. It must be
distinguished from frank fresh blood loss caused by
partial separation of the placenta or a ruptured vasa
praevia.
8. Appearance of the presenting part
Excessive moulding of the fetal head may result in the
formation of a large caput succedaneum which can
protrude through the cervix prior to full dilatation of the os.
Very occasionally, a baby presenting by the vertex may be
visible at the perineum at the same time as remaining
cervix.
This is more common in women of high parity. Similarly a
breech presentation may be visible when the cervical os is
only 7–8 cm dilated.
B. Confirmatory evidence
In many midwifery setings, it is held that a vaginal
examination must be undertaken to confirm full
dilatation of the cervical os. This is both to ensure
that a woman is not pushing too early, and to
provide a baseline for timing the length of the
second stage of labour.
Phases and duration of the second stage
Two distinct phases in second stage progress have
been recognized in some women. These are the
latent phase, during which descent and rotation
occur, and the active phase, with descent and the
urge to push.
The latent phase
In some women, full dilatation of the cervical os is recorded, but the
presenting part may not yet have reached the pelvic outlet. Women in
this situation may not experience a strong expulsive urge until the head
has descended sufficiently to exert pressure on the perineal tissues. It is
hypothesized that the prolongation of second stage progress when
epidural analgesia is used is due to the relaxation effect of epidural
analgesia on the pelvic floor muscles, meaning that the fetal presenting
part does not encounter the necessary resistant force from the pelvic
floor to bring about the normal rotation process. This tends to be
particularly evident in nulliparous women. Passive descent of the fetus
can continue with good midwifery support for the woman until the head is
visible at the vulva, or until the woman feels a spontaneous desire to
push.
The active phase
Most women without epidural analgesia will experience a compulsive
urge to push, or bear down, once the fetal head has rotated and started
to descend. The phase of labour that involves active bearing down is
termed the active second stage of labour.
Duration of the second stage
There is no good evidence about the absolute time limits of
physiological labour. The second stage of labour can last for up to three
hours or so before the risk of maternal and/or fetal compromise begins
to increase.
In the presence of regular contractions, maternal and fetal wellbeing,
and progressive descent, considerable variation between women is to
be expected.
Maternal response to transition and the second stage
Pushing
Traditionally, if the maternal urge to push occurs before
confirmation of full dilatation of the cervical os, or the
appearance of a visible vertex, the mother has been
encouraged to avoid active pushing. This has been done
to conserve maternal effort and allow the vaginal tissues
to stretch passively. Techniques to avoid active pushing
efforts in this situation include:
 position change, left lateral.
 using controlled breathing.
 inhalation analgesia.
 or even narcotic or epidural pain relief.
Position
If the woman lies flat on her back, resulting in hypotension.
This can lead to reduced placental perfusion and
diminished fetal oxygenation. The semi-recumbent or
supported siting position, with the thighs abducted, is the
posture most commonly used in Western cultures. While
this may afford the midwife good access and a clear view of
the perineum, the woman's weight is on her sacrum, which
directs the coccyx forwards and reduces the pelvic outlet.
In addition, the midwife needs to bend forward and laterally
to support the birth, which may lead to injury.
Left lateral position
This position was widely used in the United Kingdom (UK)
in the 20th century, although it is less common in current
practice. The perineum can be clearly viewed and uterine
action is effective, but an assistant may be required to
support the right thigh, which may not be ergonomic. It
provides an alternative for women who find it difficult to
abduct their hips. It may also aid fetal rotation, especially in
the context of epidural analgesia (Downe et al 2004).
Upright positions: squatting, kneeling, all-fours, standing, using
a birthing ball
Many women find that being upright – whether kneeling, sitting,
squatting, or even standing – is more comfortable than lying down at
this point. Plus, it may put gravity to work for you.
These included reduced duration of second stage labour, fewer
assisted births, fewer episiotomies, reduced severe pain in second
stage labour, and fewer abnormal heart rate paferns.
However, increased rates of perineal damage and of estimated blood
loss >500 ml also occurred. There are a number of studies relating to
positions and mobility for women using so-called ‘walking epidurals’,
but recent data on the physiology of labour and birth for women in
spontaneous labour who mobilize without the use of pharmacological
pain relief do not seem to exist.
Radiological evidence demonstrates an average increase of 1 cm in the
transverse diameter and 2 cm in the anteroposterior diameter of the
pelvic outlet when the squafing position is adopted. This produces an
average 28% increase in the overall area of the outlet compared with the
supine position (Russell 1969).
Some women find the all- fours position to be the optimum approach for
all or part of their labours, especially in the case of an occipitoposterior
position, due to relief of backache.
It is important not to insist on any position as the ‘right’ one.
Positive and dramatic effects on labour progress can be achieved
by encouraging the woman to change and adapt her position in
response to the way her body feels.
. A full understanding of the mechanism of labour
should enable the midwife to adapt to any position
that the woman wishes to adopt, ensuring in the
process that the postures adopted by the midwife
are protective of her own health (and, specifically, of
her back).
Maternal and fetal condition
If the woman has had analgesia, or if there is any
concern about her wellbeing or that of her baby,
then more frequent or continuous monitoring may
limit the choices available to her. However, there
are often creative solutions to these situations,
and good midwifery care involves finding these
solutions where possible.
The mechanism of normal labour (cephalic presentation)
As the fetus descends, soft tissue and bony structures exert pressures
that lead to descent through the birth canal by a series of movements.
Collectively, these movements are called the mechanism of labour
. Knowledge and recognition of the normal mechanism enables the
midwife to anticipate the next step in the process of descent.
Understanding and constant monitoring of these movements can help to
ensure that normal progress is recognized, that the woman gives birth
safely and positively, or that early assistance can be sought should any
problems occur.
. Principles common to all mechanisms are: descent takes place.
At the onset of labour the
most common presentation is
the vertex and the most
common position either left
or right occipitoanterior;
therefore it is this mechanism
which will be described. In
the lie is longitudinal
the presentation is cephalic
this instance:
the position is right or left
the presenting part is the
occipitoanterior
posterior part of the anterior
the attitude is one of good
parietal bone.
flexion
the denominator is the occiput
Main movements of the fetus
Descent
Descent of the fetal head into the pelvis often begins before
the onset of labour. For a primi-gravid woman this usually
occurs during the later weeks of pregnancy. In multigravid
women muscle tone is often more lax and therefore descent
and engagement of the fetal head may not occur until labour
actually begins.
Following rupture of the forewaters and the exertion of
maternal effort, progress speeds up.
Flexion
This increases throughout labour. pressure exerted down
the fetal axis will be more forcibly transmitted to the occiput
than the sinciput.
The effect is to increase flexion which results in smaller
presenting diameters that will negotiate the pelvis more
easily. At the onset of labour the suboccipito-frontal
diameter, which is approximately 10 cm, is presenting. With
greater flexion, the sub-occipitobregmatic diameter, that is,
approximately 9.5 cm, presents.
Internal rotation of the head
During a contraction, the leading part is pushed
downwards onto the pelvic floor. The resistance of this
muscular diaphragm brings about rotation. As the
contraction fades, the pelvic floor rebounds, causing the
occiput
to
glide
forwards. As
discussed
above,
resistance is an important determinant of rotation, as
demonstrates. This explains why rotation is often
delayed following epidural analgesia, which causes
relaxation of pelvic floor muscles.
Extension of the head
Once crowning has
occurred, the fetal head
can extend, pivoting on
the suboccipital region
around the pubic bone.
This releases the
sinciput, face and chin,
which sweep the
perineum, and then are
born by a movement of
extension,
(A) Birth of the head. (B) Restitution. (C) External
rotation
Restitution
The twist in the neck of the fetus which resulted from internal rotation is
now corrected by a slight untwisting movement. The occiput moves of a
circle towards the side from which it started.
Internal rotation of the shoulders
The shoulders undergo a similar rotation to that of the head to lie in the
widest diameter of the pelvic outlet, namely anteroposterior. The anterior
shoulder is the first to reach the levator ani muscle and it therefore
rotates anteriorly to lie under the symphysis pubis. This movement can
be clearly seen as the head turns at the same time (external rotation of
the head). It occurs in the same direction as restitution, and the occiput
of the fetal head now lies laterally.
Lateral flexion
When the woman is in a supported siting position, the
anterior shoulder is usually born first, although midwives
who encourage women to adopt an upright or kneeling
positions have observed that the posterior shoulder is
commonly seen first. In the former case, the anterior
shoulder slips beneath the sub-pubic arch and the posterior
shoulder passes over the perineum. In the later the
mechanism is reversed. This enables a smaller diameter to
distend the vaginal orifice than if both shoulders were born
simultaneously.
Midwifery care in transition and the second stage
Observations during the second stage
Four factors determine whether the second stage is
continuing safely, and these must be carefully
monitored:
Uterine contractions
Descent, rotation and flexion of the presenting part
Fetal condition/suspicious or pathological changes
in the fetal heart
Maternal condition.
Uterine contractions
The strength, length and frequency of contractions
should be assessed regularly by observation of
maternal responses, and by uterine palpation
during the second stage of labour.
They are usually stronger and longer than during
the first stage of labour, with a shorter resting
phase.
Fetal condition/suspicious or pathological changes of
the fetal heart
If the membranes are ruptured, the liquor is observed to
ensure that it is clear. While thin old meconium staining is
not always regarded as a sign of fetal compromise.
The midwife should learn to recognize the normal changes
in fetal heart rate patterns during the second stage, both
when monitored continuously (where there are specific risk
factors) and when monitored intermittently. This will
minimize the risk of iatrogenic intervention, and maximize
a timely response to fetal compromise if it occurs.
If the woman is labouring normally, NICE guidelines
recommend that a Pinard's stethoscope or other hand-held
system such as a Sonic aid should be used to monitor the
fetal heart intermittently (NICE 2007). During the second
stage this is usually undertaken immediately after a
contraction, with some readings being taken through a
contraction if the woman can tolerate this.
Late decelerations, and a lack of return to the normal
baseline, a rising baseline or diminishing beat-to-beat
variation, are signs of concern.
Maternal condition
The midwife's observation includes an appraisal of the woman's ability
to cope emotionally as well as an assessment of her physical wellbeing.
This includes close attention to what she says, as well as how she
behaves, and a with supportive response to any indication that she is
losing belief in herself to accomplish the birth of her baby.
Maternal pulse rate is usually recorded half-hourly and blood pressure
every few hours, provided that these remain within normal limits. If the
woman has an epidural in situ, blood pressure will be monitored more
frequently, and continuous electronic fetal monitoring will probably be in
use.
Maternal comfort
As a result of her exertions the woman usually feels very hot and sticky,
and she will find it soothing to have her face and neck sponged with a
cool flannel. Her mouth and lips may become very dry. Sips of iced
water or other fluids are refreshing and a moisturizing cream can be
applied to her lips. Her partner may help with these tasks as a positive
contribution to ease her discomfort.
The bladder is vulnerable to damage, due to compression of the bladder
base between the pelvic brim and the fetal head. The risk is increased if
the bladder is distended. The woman should be encouraged to pass
urine at the beginning of the second stage unless she has recently done
so.
Preparation for the birth
Once active pushing commences, the midwife should prepare for the birth.
The room in which the birth is to take place should be warm with a
spotlight available so that the perineum can be easily observed if
necessary.
A clean area should be prepared to receive the baby, and waterproof
covers provided to protect the bed and floor.
Sterile cord clamps, a clean apron, and sterile gloves are placed to hand.
In some setings, sterile gowns are also used.
An oxytocic agent may be prepared, either for the active management of
the third stage if this is acceptable to the woman, or for use during an
emergency.
A warm cot and clothes should be prepared for the baby.
Birth of the baby
The midwife's skill and judgment are crucial factors in
minimizing maternal trauma and ensuring an optimal
birth for both mother and baby.
These qualities are refined by experience but certain
basic principles should be applied. They are:
observation of progress.
prevention of infection.
emotional and physical comfort of the mother.
anticipation of normal events.
support for the normal processes of labour.
recognition of abnormal developments.
 appropriate management to complication.
Birth of the head
Once the birth is imminent, the perineum may be swabbed
clean of any mucus and a clean pad is placed under the
woman to absorb any faeces or fluids. If she is not in an
upright position a pad is placed over the rectum on the
perineum (but not covering the fourchette) and a clean
towel is placed on or near the woman for receipt of the
baby. Throughout these preparations the midwife observes
the progress of the fetus. With each contraction the head
descends. The head recedes between contractions, which
allows these muscles to thin gradually.
The skill of the midwife in ensuring that the active phase is
unhurried helps to safeguard the perineum from trauma,
either observing the gradual advancement of the fetal head
or controlling it with light support from her hand. One large
study, indicated that, compared with guarding the
perineum, a hands-off technique????? was associated
with slightly more maternal discomfort at 10 days
postnatally (McCandlish et al 1998). The hands-off
technique was also associated with a lower risk of
episiotomy, but a higher risk of manual removal of placenta.
There is some debate about the generalizability of this trial
to all sefings and positions in labour.
Most midwives place their fingers lightly on the
advancing head to monitor descent and prevent very
rapid crowning and extension, which are believed to
result in perineal laceration (see (Fig. 17.5). Excessive
pressure on the head, however, may be associated with
vaginal lacerations. Whatever technique the midwife
adopts, it should be based on the assumption that it is
the woman who is giving birth to her baby, and the
midwife is thereto add the minimum physical help
necessary at any given time.
Supporting the head. (A) Preventing rapid extension. (B) Controlling the
crowning. (C) Easing the perineum to release the face.
Once the head has crowned, the woman can achieve control by
gently blowing or ‘sighing’ out each breath in order to minimize
active pushing. Birth of the head in this way may take two or three
contractions but may avoid unnecessary maternal trauma. The
head is born by extension as the face appears at the perineum.
During the resting phase before the next contraction the midwife
may check that the cord is not around the baby's neck. If found, it is
usual to slacken it to form a loop through which the shoulders may
pass. If the cord is very tightly wound around the neck, it is
common practice in the UK to apply two artery forceps
approximately 3 cm apart and to sever the cord between the two
clamps (Jackson et al 2007).
Once the head has crowned, the woman can achieve control by
gently blowing or ‘sighing’ out each breath in order to minimize
active pushing. Birth of the head in this way may take two or three
contractions but may avoid unnecessary maternal trauma. The
head is born by extension as the face appears at the perineum.
During the resting phase before the next contraction the midwife
may check that the cord is not around the baby's neck. If found, it is
usual to slacken it to form a loop through which the shoulders may
pass. If the cord is very tightly wound around the neck, it is
common practice in the UK to apply two artery forceps
approximately 3 cm apart and to sever the cord between the two
clamps (Jackson et al 2007).
Birth of the shoulders
Restitution and external rotation of the head maximizes
the smooth birth of the shoulders and minimizes the risk
of perineal laceration. However, it is not uncommon for
small babies, or for babies of multiparous women, to be
born with the shoulders in the transverse, or even to
have a twist in the neck opposite to that expected. While
the hands-on technique in the HOOP trial included both
perineal support and active birth of the trunk and
shoulders (McCandlish et al 1998
it is not clear which component of this technique was
beneficial for women and babies. If the position is
upright, it is more common for the shoulders to be left
to birth spontaneously with the help of gravity.
During a water birth, it is important not to touch the
emerging fetus to avoid stimulating it to gasp
underwater. If there is a problem with the birth in this
circumstance, the woman should be asked to stand up
out of the water before any manoeuvres are
attempted.
One shoulder is released at a time to avoid overstretching
the perineum. A hand is placed on each side of the baby's
head, over the ears, and gentle downward traction is
applied (Fig. 17.7). This allows the anterior shoulder to slip
beneath the symphysis pubis while the posterior shoulder
remains in the vagina.
If the third stage of labour is to be actively managed, the
assistant will now give an intramuscular (IM) oxytocic drug.
When the axillary crease is seen, the head and trunk are
guided in an upward curve to allow the posterior shoulder
to escape over the perineum.
These manoeuvres are reversed if the mother is in a
forward-facing position such as all-fours. The midwife or
mother may now grasp the baby around the chest to aid
the birth of the trunk and lih the baby towards the mother's
abdomen. This allows the mother immediate sighting of
her baby and close skin contact, and removes the baby
from the gush of liquor which accompanies release of the
body. If the midwife does not actively assist, she should be
ready to support the head and trunk as the baby emerges.
The time of birth is noted and recorded
(A) Downward traction releases the anterior shoulder. (B) An upward curve
allows the posterior shoulder to escape.
If this has not already been done, the cord is
severed between two cord clamps placed close to
the umbilicus at whatever time is considered
appropriate, with due afention to the theories
around the blood volume model set out above.
The cord clamp is applied. The baby is dried and
placed in the skin-to-skin position with the mother
if she is happy with this (Moore et al 2007;
Bystrova et al 2009). A warm cover is placed over
the baby.
Swabbing of the eyes and aspiration of mucus during
and immediately following birth are not considered
necessary providing the baby's condition is satisfactory.
Oral mucus extractors should not be used because of
the risks of mucus that is contaminated with a virus such
as hepatitis or human immunodeficiency virus (HIV)
entering the operator's mouth.
The moment of birth is both joyous and beautiful. The
midwife is privileged to share this unique and intimate
experience with the parents.