What happens during labour

Labour is defined as the process of childbirth by which uterine contractions bring about the expulsion of the fetus in a term pregnancy (which is usually 37 weeks – 42 weeks from last menstrual period).

In response to uterine contractions, the lower segment of the uterus stretches and thins. This enables the cervix to dilate and the birth canal is formed through which the fetus descends into the pelvis  and is delivered vaginally. Labour is accompanied by different processes that follow one another with which a normal labour can be diagnosed. In the absence of these processes, the labour is termed abnormal labour.

PROCESSES OF A NORMAL LABOUR 

The processes that occur during normal labour are responsible for the successful delivery of the fetus at term pregnancy. They can clearly be identified and observed through the period in which labour lasts.

Lightening 

The process of labour begins with a phenomenon called lightening which refers to the descent of the uterus deeper into the lower abdomen. This happens usually at 37 weeks of pregnancy and is noticed more easily in a woman who is pregnant for the first time.

Contractions 

After 37 weeks gestation, what follows lightening of the uterus are uterine contractions. Any form of uterine contractions before the 37th week is termed as Braxton Hicks contractions which are mild, painless, non rhythmic, irregular and non frequent. This is also known as false labour because the contractions are not strong enough to initiate the opening of the cervical os. When Braxton Hicks contractions become more painful and rhythmic before the 37th week of pregnancy, it is an indication of what is called preterm labour. Preterm labour is a complication of labour and the fetus must be delivered immediately if that happens and life support technique administered for the baby’s survival.

True labour however, is indicated by uterine contractions which are painful, rhythmic, long lasting, and frequent especially at 37 weeks gestation or more and accompanied by the opening of the cervical os. The onset, intensity, frequency and duration of such contractions are noted down by the midwife or obstetrician.

Cervical effacement 

What follows uterine contractions during labour is the opening of the cervical os. The cervical os during pregnancy is covered by mucus membrane which serves to prevent microbial attack into the uterus. During labour, the mucus membrane may burst open releasing mucus plug, but this may not be observed by all women.  Sometimes, the mucus discharge occurs simultaneously with the bloody show.

Bloody show 

The dilatation of the cervical os especially in the active phase of the first stage of labour is accompanied by the passage of blood. This blood may mix with mucus from the mucus membrane. This bloody show is dark red in colour but may also be pinkish.

Rupture of membranes 

True labour occurring at 37 weeks or more is accompanied by the rupture of the amniotic membrane releasing amniotic fluid from the uterus through the vagina. This process is what has more commonly been termed as “water bursting.” This fluid is examined by the obstetrician for the presence of meconium which is an indicator for fetal distress. After the rupture of the membrane, delivery of the fetus takes place shortly after.

Premature rupture of membrane can occur before 37 weeks gestation as a complication of labour. When this happens, nothing can be done to repair the ruptured membrane and as such the fetus must be delivered by stimulating or inducing contractions medically, if natural contractions are absent.

STAGES OF LABOUR 

The entire process of labour occurs in stages which are all as a result of uterine contractions. There are three (3) stages of labour and are summarised as follows.

First stage of labour 

The first stage of labour starts from the onset of uterine contractions to the time when the cervix is completely effaced. It consists of cervical dilatation which is at the rate of about 1cm per hour and occurs in 2 phases:

  1. Latent phase : Lasts for about 3 – 8 hours which last longer in first time pregnancy with the cervical opening of between 0cm – 3cm.
  2. Active phase : cervical opening in the active phase is from 3cm – 10cm.

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The effects of the increasing uterine contractions which produces cervical dilatation becomes obvious in the woman’s appearance. She is looks preoccupied and slips into a breathing pattern she has learned. She may become distressed and membrane can rupture at the first stage.

Second stage of labour 

The second stage begins from when the cervix is fully dilated to when the fetus is expelled through the cervical canal and vagina. The normal second stage lasts  for about an hour in first pregnancies and may be less in multi parous women. It is recognised by a change in the character of uterine contractions. They become more powerful and expulsive. Secondary forces like the diaphragm are active, the woman holds her breath and the abdominal muscles contract.

Sometimes the woman may feel nauseated and vomit. She may also feel that the bowel is about to move due to the pressure on the rectum which can inhibit her cooperation unless the reason is explained to her. The head of the fetus at this stage descends deeply in the pelvis and may be visible or palpable through the perineum.

Third stage of labour 

This is the period from the delivery of the fetus to the delivery of the placenta. The descent and delivery of the fetal head brings the shoulders of the fetus into the pelvic cavity. The head then moves in a natural position relative to the shoulder in the process called restitution. There is also a rotation of the fetal head after its delivery which makes the occiput of the head to lie next to the left maternal thigh in the process called external rotation. The anterior shoulder can now slip under the pubis and with lateral flexion of the fetal body, the posterior shoulder is delivered and the rest of the body follows easily. The umbilical cord is cut and placenta delivery takes place.

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Summary of second and third stages of labour

Placental delivery is most commonly done through the Brandt-Andrews method, where the separated placenta is removed by traction of the cord with one hand while the other hand maintains pressure upwards on the funds of uterus until placenta appears in the vulva where it is caught with both hands and membranes twisted gently to allow them peel off completely.

The postnatal careand management of the mother commences immediately after this stage as well as the post delivery or neonatal  care and management of the new born baby.

 

 

REFERENCE 

Kelvin P. Hanretty : “Normal Labour” Obstetrics Illustrated (6th edition).

Geoffrey Chamberlain : “Normal Labour” Obstetrics by Ten Teachers (16th edition)

 

 

 

 

 

 

 

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