The third pregnancy ultrasound is normally the last virtual meeting before the actual meeting with the baby on the day of delivery. It is essential to control the good growth of the baby and to prepare for the birth.

The third and last pregnancy ultrasound takes place around 32 WA (end of the 7th month, beginning of the 8th). It is not compulsory but is part of the examinations systematically prescribed for all pregnant women and highly recommended.

You do not need to be fasting or have a full bladder for this test. On the other hand, it is not recommended to put cream on the stomach during the 48 hours preceding the ultrasound because this can affect the transmission of ultrasound and the quality of the image.

The procedure is that of a classic ultrasound: the practitioner begins by coating the belly of the mother-to-be with a gel in order to facilitate the passage of the ultrasounds. Then, he will move the probe on the tummy in order to obtain different images of the baby, observe specific parts and take several key measurements.

At this stage of pregnancy, the baby measures approximately 38 cm from head to heels for 1,5 kg (1). It is now larger than the probe, so it is no longer possible to see it in full on the screen.

Her body slowly rounds off thanks to the fatty tissue that gradually accumulates under her skin. By birth, he will double his weight again. In the uterus, which now extends to the mother’s ribs, it takes up a lot of space and there is much less amniotic fluid than on the second ultrasound.

The fetus is sensitive to sounds, to light, to touch. His kidneys, his stomach, his intestines are working; they treat the amniotic fluid that it absorbs in large quantities.

On the screen, we can now make out his hair – if indeed he has any.

During this ultrasound at the end of pregnancy, the practitioner checks various elements:

• baby growth by performing a biometry, that is to say by measuring different key areas of the baby: the biparietal diameter (or BIP, corresponds to the space between the two parietal bones of the baby’s face), the cranial perimeter (PC) , abdominal perimeter (PA), femoral length (LF) and transverse abdominal diameter (DAT). The results are then compared to a growth curve;
• the baby’s morphology in order to check the good evolution of the organs since the second ultrasound. The brain (to control furrows and cerebral gyration), the heart (the size of the cavities and the proper functioning of the valves and flaps) and the kidneys (to check for possible renal dilation) are subject to careful examination because they develop later in pregnancy;
• baby’s vitality via its movements, its swallowing;
• the baby’s position or “presentation”; at this stage of the pregnancy, it has normally turned and is presented upside down, the ideal position for childbirth;
• the position of the placenta and its degree of maturity, because an aging placenta risks no longer fulfilling its nourishing role;
• the amount of amniotic fluid ;
• blood flow of certain arteries thanks to fetal doppler.

Depending on the information gathered during this ultrasound, the doctor or midwife can establish a prognosis as to the progress of the birth and take various measures if necessary. Are taken into account:

• the baby’s position: if the baby is in a breech, it is possible that he will turn around before term, but this is still difficult given the little space he has left. An ultrasound will be performed around 35 WA to check the baby’s position. If it is still in siege, an external maneuver version (VME) can be attempted. Performed in the hospital around 37 WA under ultrasound control and monitoring, this technique consists of placing one hand on the baby’s buttocks and the other on his head in order to rotate him on his axis and put him in the head-down position. . The success rate for this maneuver is 39 to 65% according to the medical literature (2). A fetal version by acupuncture can also be tried. It is based on a specific point, point V67, located at the end of the little toe. If the baby is still in breech, a low approach can be tried according to the dimensions of the maternal pelvis (evaluated by pelvimetry), the size of the baby, the flexion of his head. Childbirth, considered risky, will be done by a doctor and in the presence of a pediatrician and an anesthesiologist. If the vagina seems difficult and risky, a cesarean section will be scheduled.
• Estimation of fetal weight: the various biometric measurements are entered into software which makes it possible to estimate fetal weight at birth, with a margin of error of approximately 10% (3). If a macrosomia (heavy baby) is suspected and if the mother has a so-called “borderline” pelvis, radiopelvimetry or pelviscan will be prescribed in order to evaluate the pelvic measurements.
• insertion of the placenta: in the event of a covering placenta previa (the placenta completely covers the opening of the cervix), a cesarean section will be scheduled because birth is impossible vaginally.

In some cases, a follow-up ultrasound will be performed after a few weeks. This is particularly the case when uterine growth retardation (IUGR) is detected. When IUGR is severe and puts the baby’s survival at risk, a cesarean section may be performed to deliver the baby as soon as possible.

Finally, this third ultrasound may reveal a late-onset fetal morphological anomaly, particularly at the cardiac or renal level. A specific follow-up will then be set up for the rest of the pregnancy but also for after birth, with when necessary and possible, a surgical intervention scheduled from the first weeks of life.