Adverse pregnancy outcomes in deliveries prior to, at and beyond 39 weeks; low- and high-risk women.

Background: Hypertensive disorders are associated with maternal and neonatal complications. Though they are more common in women with history of prior preeclampsia, they can occur in uncomplicated pregnancies.

Objective: To determine the proportion of adverse pregnancy outcomes in deliveries prior to or at ≥39 weeks, in uncomplicated singleton nulliparous women (low-risk), as well as women with history of preeclampsia in a prior gestation (high-risk).

Study Design: This was a secondary analysis from the multicenter trials of low dose aspirin for preeclampsia prevention in low and high-risk pregnancies. The proportion of adverse pregnancy outcomes including hypertensive disorders in pregnancy, small for gestational age, placental abruption, neonatal intensive critical unit admission, and respiratory distress syndrome were evaluated in the two groups. Adverse pregnancy outcomes were stratified by gestational age at delivery (<39 weeks and ≥39 weeks). Descriptive statistics were performed, and results reported as percentages.

Results: Three thousand twenty-one pregnancies were included in the low risk group, and 600 in the high risk one. In the low risk group 362 (12%) had hypertensive disorders, with 58% occurring at ≥39 weeks. In the low risk group, the rate of small for gestational age was of 5.9%, placental abruption 0.4%, neonatal intensive care unit admission 9%, and respiratory distress syndrome 3.5%. Sixty percent of all small for gestational age, 31% of all placenta abruptions, 44% of all neonatal intensive care unit admissions and 33% of respiratory distress syndrome cases, occurred at ≥39 weeks in the low risk group. In contrast in the high risk group, 197 (33%) patients developed a hypertensive disorder, with 35.5% occurring at ≥39 weeks. The overall rate of small for gestational age was 9.2%, abruption 2%, neonatal intensive care unit admission 15.5%, and respiratory distress syndrome 5%. In this group, 24% of all small for gestational age, 8.3% of all placental abruptions, 16% of all neonatal intensive care unit admissions and 3% of respiratory distress syndrome cases, were at ≥39 weeks.

Conclusions: We found that in low-risk women, the majority of hypertensive disorders occur at ≥39 weeks, whereas in women with prior preeclampsia the majority develops at <39 weeks. Moreover, a third of all placental abruption occurred at or beyond 39 weeks in the low risk group. Our findings suggest that in low-risk women, a policy of delivery at 39 weeks may prevent most of the adverse outcome that occurs beyond that gestational age cutoff.