Prolonged and post-term pregnancies: guidelines for clinical practice from the French College of Gynecologists and Obstetricians (CNGOF)

The duration of pregnancy varies between 40(+0) and 41(+3) weeks. Conventionally, and essentially arbitrarily, a pregnancy is considered to be "prolonged" after 41(+0) weeks, but the infant is not considered "post-term" until 42(+0) weeks (Professional consensus). A term birth thus occurs during the period from 37(+0) to 41(+6) weeks. In France, prolonged pregnancies (≥41(+0)weeks) involve 15-20% of pregnant women, and post-term pregnancies (≥42(+0) weeks) approximately 1%. The frequency of post-term pregnancies is very heterogeneous: in Europe and the United States, it ranges from 0.5% to 10% according to country. In prolonged pregnancies, the cesarean section rate-especially the emergency cesarean rate-is multiplied by approximately 1.5 (grade B). From 37(0-6) to 43(0-6) weeks, the risk of perinatal mortality increases regularly, from 0.7‰ to 5.8‰. Meconium aspiration syndrome is responsible for substantial morbidity and mortality, and its incidence increases regularly between 38(+0) and 42(+6) weeks, from 0.24‰ to 1.42‰ (grade B). Similarly, the risks of neonatal acidosis (grade B), 5-min Apgar scores less than 7 (grade B) and admissions to neonatal intensive care (grade B) increase progressively between 38(+0) and 42(+6) weeks. These risks appear to double for post-term growth-restricted newborns (grade C). Ultrasound dating of the pregnancy makes it possible to reduce the risk that it will be incorrectly considered prolonged and that labor will therefore be induced unnecessarily. To harmonize practices, if the crown-rump length (CRL) is correctly measured (this measurement should be taken between 11(+0) and 13(+6) weeks, when CRL should measure from 45 to 84mm), ultrasound dating based on it should be used to determine the official date pregnancy began, regardless of its difference from the date assumed by the patient or estimated based on the date of the last menstrual period. This rule does not apply to pregnancies by IVF, for which the date pregnancy began is defined by the date of oocyte retrieval (Professional consensus). From 37(0-6) to 43(0-6) weeks, the risk of perinatal mortality increases regularly and there is no threshold at which a clear increase in perinatal mortality becomes visible. Fetal monitoring by cardiotocography (CTG) that begins at 41(+0) weeks would cover approximately 20% of women and reduce perinatal morbidity compared with monitoring that begins at 42(+0) weeks (grade C). The frequency recommended for this monitoring ranges between two and three times a week (Professional consensus). For ultrasonography assessment, measurement of the largest fluid pocket is recommended, because measurement of the amniotic fluid index (that is, the sum of the four quadrants) is accompanied by more diagnoses of oligohydramnios, inductions of labor, and cesareans for fetal distress without any improvement in neonatal prognosis (grade A). The practice of assessing the Manning biophysical score increases the number of diagnoses of oligohydramnios and fetal heart rage (FHR) abnormalities and generates an increase in the rates of inductions and cesareans without improving neonatal prognosis. The use of this biophysical score in monitoring prolonged pregnancies is therefore not recommended (grade B). In the absence of a specific disorder, induction of labor can be proposed in patients between 41(+0) and 42(+6) weeks (grade B). Nonetheless, the choice of prolongation beyond above 42(+0) weeks appears to involve an increase in fetal risk, which must be explained to the patient and balanced against the potential disadvantages of induction (Professional consensus). Stripping the membranes can reduce the duration of pregnancy by increasing the number of patients going into labor spontaneously during the week afterward (grade B). Compared to an expectant approach, it does not increase the cesarean section rate (grade A). It reduces recourse to induction by 41% at 41(+0) weeks and by 72% at 42(+0) weeks (grade B), without increasing the risk of either membrane rupture or maternal or neonatal infection (grade B). Used as a tampon or vaginal gel, prostaglandins E2 (PGE2) are an effective method of inducing labor (grade A). They can be used to induce labor successfully, regardless of cervical ripeness (grade A). If misoprostol is chosen, the lowest dose is to be preferred, starting with a vaginal dose of 25μg every 3-6h (grade A). For misoprostol, more powerful studies remain necessary for better defining the doses, routes of administration, tolerance and indications. Misoprostol at any dose is contraindicated in women with uterine scars (grade B). Placement of an intracervical Foley catheter is an effective mechanical means of inducing labor, with less uterine hyperstimulation than prostaglandins and no increase in the cesarean section rate (grade A). Nonetheless, as the risk of infection might be increased, this technique requires more robust evaluation before entering general practice (grade B). In cases of meconium-stained amniotic fluid, pharyngeal aspiration before delivery of the shoulders is not recommended (grade A). The team managing a post-term newborn with meconium-stained amniotic fluid at birth must know how to perform intubation and, if the intubation is not helpful, endotracheal aspiration (grade C) and ventilation with a mask. Routine endotracheal intubation of a vigorous newborn is not recommended (grade A).