Advanced maternal age labor induction not associated with increased cesarean section rate: The 35/39 trial

1. Nulliparous women over 35 years of age were randomized to labor induction between 39 weeks 0 days and 39 weeks 6 days or expectant management.

2. There were no significant differences between groups in terms of the percentage of women who ultimately underwent cesarean section (primary outcome), the maternal experience of childbirth, or in the frequency of adverse maternal or neonatal outcomes.

Evidence Rating Level: 1 (Excellent)

Study Rundown: In recent decades, the average age of women at childbirth has been increasing in many industrialized nations. Childbirth at advanced maternal age (defined as 35 years or older) has been associated with increased risk of a number of maternal and neonatal adverse effects (including still births) as well as an increased likelihood of obstetrical intervention, including cesarean section. The 35/39 trial was a multicenter trial conducted at National Health Service (NHS) hospitals in the United Kingdom (U.K.) in which 619 nulliparous women of age 35 years or older were randomized either to expectant management (waiting until the spontaneous development of labor or development of a medical problem mandating induction) or induction of labor between 39 weeks 0 days and 39 weeks 6 days. There were no significant differences between groups in terms of the percentage of women who ultimately underwent cesarean section (primary outcome), the maternal experience of childbirth, or in the frequency of adverse maternal or neonatal outcomes.

The trial draws strength from its randomized, controlled design, adding to a relative dearth of data; many previous trials of induction at or near term have involved women with established complications of pregnancy, which were largely excluded from this study. The results are largely limited by the homogenous, largely white, composition of the study participants, and the fact that it was carried out in one country’s health system, limiting its generalizability.

Click to read the study in NEJM

Relevant Reading: Induction of labor at full term in uncomplicated singleton gestations: a systematic review and meta-analysis of randomized controlled trials

In-Depth [randomized controlled trial]: The 35/39 trial was a randomized, controlled trial involving 39 sites in the NHS in the U.K. and originally screened 6,455 nulliparous women over the age of 35 for eligibility; 619 were randomized either to expectant management or induction of labor between 39 weeks 0 days and 39 weeks 6 days. Exclusion criteria included known fetal congenital abnormalities or contraindications to labor, vaginal delivery, or expectant management (e.g. gestational diabetes). The groups were well balanced. In terms of the primary outcome of cesarean section rates, there was no significant difference between groups (RR=0.99; 95% [CI]: 0.87 to 1.14). Similarly, there were no significant differences in terms of rates of assisted vaginal delivery (p=0.08), or in terms of secondary outcomes including postpartum hemorrhage (p=0.47 for comparison), shoulder dystocia (p=0.45), requirement of blood transfusion (p=0.16), or neonatal outcomes. 83% of trial participants completed the Childbirth Experience Questionnaire, and there were no significant differences between groups in terms of childbirth experience.

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