The Onset of Labor
During pregnancy the uterine muscle contracts intermittently and the
uterus as a whole becomes hard, usually without causing any
discomfort. Indeed, the mother-to-be may not be aware that
this is occurring. In late pregnancy these contractions become more
frequent and powerful and the mother-to-be may feel them and be
deceived into believing that labor has started. This phenomenon,
called 'false labor', is more common in women who are having a
second or subsequent baby and may cause an unnecessary trip to the
Beginning Stages of Labor
True beginning stages of labor is when the uterine contractions become regular and
cause a progressive dilatation (opening up) of the cervix and
descent of the foetus through the pelvis. As a result of dilatation
commencing the membranes around the internal os (opening) of the
from their attachment and slight bleeding occurs. Sometimes this
slight bleeding or 'show', as it is called, is the first thing that
a woman notices. The contractions then become obvious later.
Occasionally, rupture of the membranes, in which a small amount of
fluid is released, is the first obvious sign that labor has
The most usual sequence of events is the onset of regular
contractions followed by a slight blood loss. Rupture of the
membranes does not normally occur until a later stage.
What Causes Labor to Begin?
The onset of labor represents the
culmination of a series of complicated hormonal changes that are
instituted by the foetus itself. The exact mechanism in the human
being is not known, but the hormone, oxytocin, and the substances
known as prostaglandins, play an important part in making the uterus
When to go to the Hospital?
In most cases the onset of labor will be clearly recognized.
Sometimes, however, the mother-to-be is uncertain and delays going
into hospital. In practice, as soon as regular contractions, say one
in every ten minutes, have occurred for more than one hour, labor
should be assumed to have started even if no bleeding has occurred
and the membranes have not ruptured. Slight bleeding alone is not
strong enough evidence and, in this instance, the mother-to-be
should wait for the contractions to begin before going in to
hospital. Rupture of the membranes, however, is always a clear
indication that the baby is on the way and the mother-to-be should
go to the hospital. If there is any doubt about whether or not
labor has started, a telephone call, asking for advice, should be
made to the doctor, or midwife, or labor ward sister at the
hospital. The important principle is: if in doubt, go in. Going in
on a false alarm is far wiser than being delivered in an ambulance!
The Stages of Labor
Traditionally, labor is divided into three stages. The first stage
extends from the onset of labor until the time when the cervix is
fully dilated, that is when the cervix is sufficiently open to allow
the foetal head to pass through. When the cervix is fully dilated,
the first stage has come to an end.
The second stage of labor lasts from
full dilatation of the cervix until the completion of delivery of
The third stage of labor extends from
the time of the completion of the delivery of the baby until the
completion of the delivery of the placenta. The duration of
the first stage of labor varies considerably, but a first stage
which lasts from four to twelve hours would be considered normal for
a primipara (a mother giving birth to her first baby) or two to six
hours for a multi-para (a mother who has had more than one baby).
There is a good deal of individual variation, however, and shorter
or longer labors occur.
The duration of the second stage of
labor should never be longer than two hours and it is often much
shorter, especially for second or subsequent babies. The duration of
the third stage of labor is shortened in modern obstetric practice
by an injection which causes a very powerful contraction of the
uterus. This helps to expel the placenta and, as a result, the third
stage of labor rarely lasts more than five minutes.
Dilation of the Cervix
The uterine muscle is stronger in the upper segment of the uterus
than in the lower segment. As a result, when the uterus contracts,
the stronger upper segment draws the lower segment and cervix up
over the foetal head and, at the same time, drives the head
downwards into the pelvis: Continuing contractions then stretch and
dilate the os (opening) until the opening is large enough to allow
the baby's head to pass through.
Sequence of Events
1. Towards the end of the pregnancy, the
baby is usually positioned head downwards in the uterus vertex presentation.
2. At the very start of the first stage of labor, the baby's head
begins to descend. The cervix is flattening out, sometimes called
3. During the first stage of labor, the strong contractions of the
uterine muscles gradually dilate the cervix. The membranes have
4. By the end of the first stage of labor, the
cervix is fully dilated— ten centimeters or five fingers breadths.
This marks the beginning of the second stage of labor, the birth of
the baby. The baby's head can be seen by the obstetrician or the
midwife and the mother feels a strong desire to push downward with
5. The uterine contractions, combined with the mother's efforts,
push the baby down the vagina. Most of the work in the second stage
of labor is involved with the birth of the head. Once the head is
born, face downwards, it turns and the shoulders and body slip out
6. In the third stage of labor, the placenta separates from the
wall of the uterus and is delivered with just one more contraction.
7. The baby's head usually looks slightly elongated at birth
with a small swelling (caput) at the back. It soon assumes a normal
round shape. The vagina is not directly affected by the
uterine contractions, but it is very easily distended in labor and
allows the foetus to pass through without difficulty. This occurs
during the second stage of labor when the mother is playing an
active role in helping to push the foetus down in time with the
uterine contractions. This continues until the delivery is
completed. Although the vagina easily distends to allow the passage
of the baby, the vulva and lower pelvic muscles may require an
episiotomy (incision). This is easily repaired with stitches (see
below). After the birth of the baby the uterus contracts
and retracts, that is it shrinks down in size, sheering the placenta
(after-birth) from its attachment and pushing it down into the lower
uterine segment and upper vagina. From this site, the placenta is
delivered either by the obstetrician drawing on the umbilical cord,
or by the mother pushing down as she did when having the baby. Once
the placenta is delivered, labor is completed.
In general, labor takes some twelve
hours or so for a first baby and six hours or so for second and
Mechanism of Labor
In order to pass through the cervix and out through the vagina, the
foetal head has to negotiate and squeeze through the bony tunnel of
the mother's pelvis. Squeeze is the right word, for, even in normal
labor, the head is a tight fit in the pelvis. The passage of
the head is brought about by a series of movements which,
collectively, form the mechanism of labor. Firstly, the foetal head
engages in the maternal pelvis; by this is meant the passage of the
widest diameter of the foetal head through the entrance to the
pelvis. For a mother-to-be having a first baby, this normally occurs
before the onset of labor. For second and subsequent babies, it may
not occur until labor has actually started. Once labor has started
and the head has engaged it descends slowly through the pelvis,
turning as it does so. As a result, the baby is facing backwards
After the birth of the head, the baby's shoulders
also turn inside the pelvis. This causes the head to
turn to one side or the other. Once the shoulders
are born, the rest of the baby's body passes easily
Almost all of the first and second stages of
labor are spent in bringing about the birth of the
head in the manner described. The birth of the
rest of the baby's body is accomplished in less
than a minute.
Molding and Caput Because the baby's head
is such a tight fit in the mother's pelvis, it issqueezed or molded into the best possible shape
to enable it to pass through. The baby's head can
change shape in this way because, at the time of
birth, the skull bones have not fused together.
The moulding of the head gives it an elongated
appearance which is made somewhat stranger
looking by a sort of bruise, called the caput, which
develops on the top of the head during labor. Do
not worry—both the moulding and the caput
subside quickly, so that, within twenty-four to
forty-eight hours after birth, the baby's head
assumes its normal rounded shape.
Tears, Episiotomy and Stictches
A small tear of the perineum is very common,
especially during the birth of first babies. Obstetricians have long believed that if there is a chance
of anything more than a small tear developing, it
is better to make an incision-episiotomy-since
this causes much less damage to the skin tissues than a jagged tear
and is easier to stitch accurately. The vagina is always a little less tight after
having a baby, but provided excessive tearing is
avoided by the proper use of episiotomy and
provided that careful stitching is carried out, the
difference will only be slight.
Stitches are put in under a local anaesthetic and
are so placed as to draw the tissues and skin
together so that they do not have to be taken out.
The knots on the outside fall off within a few days
and may be noticed on the pad or in the bath. The
number of stitches varies greatly. Anything from
two to ten stitches is quite normal.