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Objective: To estimate the gestational age ranges that result in optimal birth outcomes for each of four risk-defined groups.Study Design: Retrospective cohort study of singleton late thirdtrimester deliveries at a large urban teaching hospital between July 1995 and September 2003. Low-risk, advanced maternal age, hypertensive and diabetic patients were identified and grouped. Rates, by day of gestation at delivery, of cesarean delivery, major maternal perineal trauma, low 5-min APGAR score and NICU admission were determined for each study group.Results: Each study group had meaningful changes in rates of obstetric outcomes as a function of gestational age at delivery and these patterns differed from group to group. A unique optimal time of delivery (OTD) was estimated for each group. The low-risk group OTD was calculated to be 37 weeks 1 day to 41 weeks 0 day; the advanced maternal age group OTD was 38 weeks 5 days to 39 weeks 6 days; the hypertension group OTD was 39 weeks 2 days to 40 weeks 1 day; and the diabetes mellitus group OTD was 40 weeks 3 days to 41 weeks 1 day. Conclusions:The OTD varied based on obstetrical risk. Strategies to increase the proportion of deliveries that occur within the OTD for specific risk-defined groups could theoretically improve birth outcomes.

Between 2007 and 2013 in the United States, the adoption of the 39-week rule caused a progressive reduction in the proportion of term births occurring before the 39th week of gestation. During the same interval the United States experienced a significant increase in its rate of term stillbirth. This study raises the possibility that the 39-week rule may be causing unintended harm. Additional studies of the actual impact of the adoption of the 39-week rule on major childbirth outcomes are urgently needed. Pressures to enforce the 39-week rule should be reconsidered pending the findings of such studies.

Objective To determine if exposure of multiparous women to a high rate of preventive labor induction was associated with a significantly lower cesarean delivery rate. Study Design Retrospective cohort study involving 123 multiparas, who were exposed to the frequent use of preventive labor induction, and 304 multiparas, who received standard management. Rates of cesarean delivery and other adverse birth outcomes were compared in the two groups. Logistic regression controlled for confounding covariates. Results The exposed group had a lower cesarean delivery rate (aOR 0.09, 0.8% vs. 9.9%, p = 0.02) and a higher uncomplicated vaginal delivery rate (OR 0.53, 78.9% vs. 66.4%, p=0.01). Exposure was not associated with higher rates of other adverse birth outcomes. Conclusion Exposure of multiparas to a high rate of preventive labor induction was significantly associated with improved birth outcomes including a very low cesarean delivery rate. A prospective randomized trial is needed to determine causality.