Danforth’s Obstetrics and Gynecology
Lisa Moore and James N. Martin, Jr.

Prolonged Pregnancy - Menagement

 A prolonged pregnancy, also commonly called postterm pregnancy, is one that has lasted longer than 42 weeks or 294 days beyond the first day of the last menstrual period.  Postdatism implies pregnancy lasting beyond the estimated due date at 40 weeks. The term “postmature” is reserved for the pathologic syndrome in which the fetus experiences placental insufficiency and resultant intrauterine growth restriction. Prolonged pregnancies have been recognized since antiquity. Hadrian, emperor of Rome from 117 to 138 A.D., decreed that a child born 11 months after the death of a husband was illegitimate. French law recognizes as legitimate a child born 300 days after the husband's death. Postdatism as a risk factor for adverse fetal outcome has been recognized since the early part of the 20th century. Whether prolongation of a low-risk pregnancy results in increased perinatal morbidity and mortality is a matter of debate.
Postdatism occurs in 3% to 12% of all pregnancies. The definition of prolonged pregnancy is, however, somewhat arbitrary and was formulated before ultrasound dating of gestation became routine. Divon and colleagues have suggested that the definition should be changed so that pregnancies =41 weeks are considered post-term. This recommendation is based on a study of over 180,000 pregnancies at 40 weeks or more in which a significant increase in perinatal mortality was seen after 41 weeks. This same finding was noted by Browne, who described perinatal mortality after 41 weeks as 10.5 per 1,000 pregnancies, doubling that at 43 weeks, and tripling that amount at 44 weeks.
Prolonged pregnancies are at risk for macrosomia resulting in shoulder dystocia and fetal injury, oligohydramnios, meconium aspiration, intrapartum fetal distress, and stillbirth. Maternal risks include trauma, hemorrhage, and labor abnormalities. Interventions for preventing or improving outcomes in low-risk, prolonged pregnancies have proven to be of minimal benefit.

The management of uncomplicated prolonged pregnancies is controversial. An adverse event in a pregnancy that has carried beyond 40 weeks seems especially difficult because it might have been avoided by simply delivering the patient. Although rare, the risk of stillbirth increases as gestational age increases. Nonetheless, available data indicate that induction and expectant management have similar outcomes, and either is suitable for managing the uncomplicated prolonged gestation.
The National Institutes of Health (NIH) sponsored a clinical trial to compare induction at 41 weeks (n = 265) to expectant management (n = 175) consisting of twice weekly NST and AFI. There were no differences in outcome between the two groups. The trial concluded that either approach was acceptable.
Active management of the prolonged pregnancy, defined as induction at 42 weeks was studied in 707 patients. Sixty-two percent of the patients labored spontaneously and 38% were induced. Perinatal mortality was 12 per 1,000. All deaths were in the spontaneously laboring group. Cesarean sections and indications for cesarean sections were similar in both groups. Meconium was present in 23% of inductions and 34% of the spontaneously laboring group. The authors concluded that routine induction at 42 weeks was justified to prevent perinatal deaths in this population.
The Parkland Group studied 56,317 pregnancies at 40, 41, and 42 weeks. Labor was induced at 42 weeks. Neonatal outcomes were similar in all groups. Sepsis and neonatal intensive care unit admission were more common in the 42-week group. Labor complications increased between 40 and 42 weeks, including length of labor and operative delivery. Their data suggest that routine induction at 41 weeks would increase labor complications with little or no neonatal benefit.
The Canadian Multicenter Post-term Pregnancy Trial was conducted at 22 hospitals, over a 5-year period. Singleton pregnancies at 41 weeks or more were assigned to induction or monitoring. In the monitored group, women were asked to perform kick counts each day. In addition, the fetuses received NSTs three times a week and AFI determinations two or three times weekly. Patients in the monitored group were delivered at 44 weeks or for maternal–fetal indication(s). Perinatal morbidity and mortality were the same for both groups.