The stages of childbirth, from labour to birth

By Cristiano Antonino On Nov 23, 2022

Childbirth is defined as the progressive dilation of the cervix associated with rhythmic contractions of the uterus itself, leading to the expulsion of the foetus and its adnexa

This definition serves to point out that cervical dilation in the absence of contractions, or contractions in the absence of cervical dilation, are pathological conditions that are not identified with childbirth itself.

How to calculate the date of childbirth

Normally, delivery is expected between the 38th and 42nd week of gestation.

The calculation of the expected date of birth is done by taking into account the first day of the last menstruation (the so-called gynaecologist’s account).

The birth that occurs before this date is called premature, the one after is called serotino.

Childbirth after the 42nd week may entail certain risks related to excessive fetal growth, so a more accurate assessment of the fetal weight is advisable.

In addition, the skin of the foetus may be more sensitive and macerated due to prolonged residence in amniotic fluid.

Preterm delivery carries greater risks related to the maturity of the foetus’ respiratory and cardiovascular systems.

Symptoms of labour

The diagnosis of labour is based on both the symptomatic finding of painful contractions and the finding of the obstetric examination.

Contractions are certainly a warning sign; in the first-time woman, small, short contractions occur during the last few weeks of pregnancy, but they have no propulsive effect on the foetus and are termed preparatory.

In the woman who has already given birth, contractions generally mark the beginning of labour.

The obstetrical examination defines the degree of preparation of the cervix: outside of labour it is retroposed (i.e. facing posteriorly) and impervious (i.e. not accessible to digital exploration).

As labour progresses, the cervix tends to align with the axis of the vagina and dilate under the pressure of the fetal head to form a single canal: uterus, cervix (disappeared) and vagina.

Contractions

Contractions are a warning sign.

They progress quite regularly and with an interval of more than 10 minutes, until they are present every 2/3 minutes in the expulsive phase.

Labour contractions are often experienced with anxiety; the contractions of the expulsive phase induce the woman to push and thus to actively cooperate.

The painful sensation results from the accumulation of lactic acid in the uterine musculature; the best way to tolerate them is good breathing; this allows the tissues to be oxygenated and the accumulation of lactic acid to be eliminated more quickly.

Natural childbirth

Physiological childbirth is a continuous and progressive process, in which mechanical, dynamic and plastic factors are traditionally identified.

Of these, the most obvious are the mechanical phenomena, i.e. the series of events that lead to the progressive descent of the foetus through the birth canal until its expulsion.

Generally speaking, we can distinguish between three phases of childbirth

a first phase that includes the engagement of the fetal head in the pelvis and the dilation of the cervix;
a second phase comprising the complete dilation of the cervix and the expulsion of the foetus;
the third stage from complete expulsion of the foetus to expulsion of the placenta.

Descent through the birth canal

The fetus, in order to undergo normal delivery, must be in cephalic presentation, i.e. with its head pointing downwards.

The first key event in the onset of delivery is the engagement of the fetal head; it is normally in a bending position and makes contact with the points where the pelvis begins to narrow.

From here follows a short descent, which further aids the flexion of the head until the contact of the chin with the sternum; the flexion movement is of fundamental importance for the further progression of the birth; with it the foetus exposes the smaller diameters of the head, i.e. it recovers space useful for its own descent.

Engagement of the fetal head in a woman in her first pregnancy can occur long before the onset of labour; in women who have already given birth it occurs later.

Once engagement, descent and flexion have occurred, the fetal head makes an internal rotation from its original position (usually transverse to the birth canal), bringing its occiput into contact with the pubic symphysis and turning its face to the sacrum.

At this point, fixing the occiput under the pubic symphysis, the head performs an extension movement, which finally allows it to exit.

In order to allow the shoulders and the rest of the foetal body to come out with as little damage as possible, the foetus makes a second rotation, this time external, whereby the shoulders are placed one under the pubic symphysis (anterior) and one towards the sacrum (posterior).

The shoulder engaged under the pubic symphysis acts as a pivot, allowing the so-called posterior shoulder to free itself first, then the second one and with it the whole fetal body easily comes out.

Once the umbilical cord is severed, we wait for the spontaneous expulsion of the placenta.

This final stage of childbirth is called secondment.

Importance of the first vagus

For nine months, the newborn breathed indirectly through the mother’s blood, without ever using her lungs.

Remember that breathing, i.e. the exchange of oxygen between air and blood, takes place at the level of the alveoli, small dilations of the pulmonary parechyma.

Until birth, the alveoli are collapsed and do not contain any air; with the first breath, a large amount of inhaled air suddenly fills them and distends them.

Once distended, the alveoli tend to remain that way for life thanks to a substance that covers them called ‘surfactant’.

This is a very thin layer of fatty acids and in particular phospholipids, produced by the lung cells themselves when they have reached a good degree of maturation.

In preterm delivery, cortisone is often administered; the function of cortisone is precisely that of a substrate for the lung cells to convert it into the surfactant components and enable the lung to reach a good degree of maturity.

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