Cervical dilation

The first phase of childbirth, the longest, corresponds to the phase of dilation of the cervix, under the action of uterine contractions, the real “engine” of labor. The contractions will act on the cervix via three mechanisms:

• increasing intrauterine pressure;
• pressing on the cervix through the water pouch or the baby’s head (or “fetal mobile”);
• by pulling directly on the cervix through the lower segment and shortening the uterine fibers.

The neck, a cylinder 3-4 cm high at the base, will gradually shorten, disappear (the internal and external orifices no longer form one) then open to reach full dilation, i.e. an opening of 10-11 cm. It will then form a single channel with the uterus.

This expansion phase is broken down into 3 stages:

• the latency phase is the initiation phase of labor. The contractions are initially irregular and not very painful, then become more rhythmic and gain in intensity. These contractions allow the cervix to soften, shorten and then open up to € 3-4 cm. This lag phase can last a few hours; it is usually longer in a woman giving birth for the first time.
• the active phase. The contractions are closer, longer and more painful. This intensification of work will allow the cervix to dilate (7-8). It is during this phase that the epidural can be placed if the mother-to-be wishes.
• the deceleration phase. Sometimes called the “phase of despair”, this phase is the shortest but the most difficult because the contractions leave little respite for the mother. The cervix is ​​fully dilated and the baby begins to descend.

In the labor room, the midwife regularly performs a vaginal examination in order to check the progress of the cervix. Fetal well-being is also continuously monitored through monitoring.

The descent and the engagement in the basin

Pushed down by the contractions, the baby descends into the pelvis, a “pipe” of elbow shape and of different perimeters. To cross these different passages, the baby will have to adapt his position while the bones of the woman’s pelvis will be able to move and separate thanks to the hyperlaxity of the ligaments due to the hormones. Depending on the women and the parity, this phase of descent can begin during dilation or at full dilation.

The baby’s descent into the pelvis follows different stages:

• engagement phase: the baby crosses the upper strait of the basin. To cross this heart-shaped passage, it must be placed diagonally in order to benefit from the larger diameter.
• descent phase: the baby descends into the middle strait, standing up straight, back forward, head flexed, chin to chest in order to present the narrowest part of his skull and pass the obstacle of the sciatic spines. At the same time, it rotates.
• release phase: the baby crosses the lower strait of the pelvis (lower opening of the pelvis).

The descent of the baby in the basin can last from 30 to 40 minutes to a few hours in the most difficult cases of deliveries and depending on the presentation of the baby and the position of the mother. The more it remains mobile and adapts its position, in particular in terms of closing or opening of the knees, the more this phase of engagement is facilitated.

Once arrived at the level of the middle strait, the baby begins to push on the perineum, then triggering the pushing reflex in the mother. It then reaches the lower strait, and walks towards the vulva, head up. Last obstacle before its release: the perineum. Helped by the mother’s pushes on the contractions, the baby’s head will stretch this bundle of muscles to cross the vulva. When the baby’s head is gripped by this muscle ring, the mother-to-be must stop pushing so as not to rush the baby out and avoid tearing the perineum. Millimeter by millimeter, the gynecologist or midwife guides the exit of the head, then once it is free, directs it downwards to free one shoulder, then upwards to free the other. The rest of the body then follows very quickly.

This last stage of childbirth is the expulsion of the placenta, membranes and umbilical cord, 15 to 20 minutes after birth. It takes place in three stages:

• Detachment of the placenta: under the effect of contractions, the uterine muscle retracts, causing the placenta to detach.
• expulsion: the placenta is expelled, helped by one or two pushes from the mother and by the pressure of the midwife’s hand on the uterine fundus. The midwife then checks that the placenta, membranes and cord are complete.
• hemostasis: all the uteroplacental vessels that previously nourished the placenta bleed, but by contracting, the uterus constricts these vessels and the bleeding eventually decreases. This step is closely monitored by the midwife to detect any onset of bleeding during delivery, a serious complication of childbirth. It is to prevent this risk that the woman is systematically kept two hours in the delivery room after childbirth.

If the placenta is not complete or if the bleeding is unusually heavy, a uterine revision is done. This gesture consists of inserting a hand into the uterus to check that there are no fragments of the placenta or membranes left.