Beginning Stages of Labor

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 hospital.

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 cervix separate  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 started.

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 probably
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 contract.

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 baby.

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 'taking up".
3. During the first stage of labor, the strong contractions of the uterine muscles gradually dilate the cervix. The membranes have ruptured.
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 each contraction.
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 fairly easily.
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 subsequent babies.


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 when born.

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 out.  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.

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