Why Repeat C-Sections Usually Wait Until 39 Weeks

What does the evidence say about scheduled repeat cesarean timing during pregnancy?

1. In a prospective U.S. registry cohort of 13,258 elective repeat cesareans without a recorded reason for earlier delivery, the composite adverse neonatal outcome occurred in 15.3% at 37 weeks and 8.0% at 39 weeks. Adjusted odds were higher at both 37 and 38 weeks compared with 39 weeks. 1
2. A secondary analysis of 23,794 term singleton repeat cesarean deliveries compared delivery in each week with pregnancy continuation. Delivery at 37 or 38 weeks had higher neonatal adverse-outcome odds, while delivery during the 39th week had lower maternal and neonatal composite odds than continued pregnancy. This observational analysis cannot remove all selection bias. 2
3. In an Australian population cohort of 17,314 low-risk patients planned for repeat cesarean at 39 to 41 weeks, 8.5% had spontaneous labor or prelabor membrane rupture before 39 weeks. Prior spontaneous preterm birth was associated with a higher rate; the estimate does not apply to every risk profile. 3
4. ACOG advises that medically indicated late-preterm or early-term delivery should not be deferred to 39 weeks when there is a clear maternal, fetal, or placental indication. Conversely, timing should not be moved earlier without an indication merely because a cesarean is planned. 4
5. For a first cesarean requested without a maternal or fetal indication, ACOG states that the operation should not occur before 39 weeks. The guidance also notes that risks such as placenta accreta spectrum and hysterectomy rise with each subsequent cesarean, so the delivery-mode discussion extends beyond timing alone. 5

Is scheduled repeat cesarean timing safe in each trimester?

• First trimester. Early prenatal care should confirm the prior cesarean history, operative details when available, and whether the current pregnancy has factors that may change delivery planning. A prior cesarean alone does not automatically justify an early-term delivery.
• Second trimester. Placental location, fetal findings, maternal disease, and candidacy for labor after cesarean become clearer as pregnancy progresses. A genuine medical or obstetric indication can change the date; an uncomplicated elective plan generally remains aimed at 39 weeks.
• Third trimester. Confirm the exact date, arrival instructions, and what to do if contractions, fluid leakage, bleeding, or decreased fetal movement occur first. Waiting for 39 weeks balances neonatal maturity against the real possibility of unscheduled labor.