Evidence Library · Timing

Why a planned cesarean waits until 39 weeks

Delivering one or two weeks earlier measurably harms newborns.

Among 24,077 scheduled repeat cesareans, newborns delivered at 37 weeks had roughly twice the odds of a serious problem compared with those delivered at 39 weeks, and those delivered at 38 weeks had about 1.5 times the odds. Individual outcomes such as breathing problems, ventilation, infection, low blood sugar, intensive care admission and a hospital stay of five days or more were all more common.

That study reports the comparison as odds rather than as absolute percentages week by week. For a sense of absolute scale, a separate series of 33,289 term births found newborn breathing problems in 35.5 per 1,000 births after a cesarean before labor, compared with 5.3 per 1,000 after vaginal birth.

US guidance is that a delivery without a medical reason should not be scheduled before 39 weeks.

If your cesarean is offered at 38 weeksAsk what the medical indication is. "It fits the schedule" and "the doctor is on call that week" are not medical indications.

Where this comes from:

334. Tita ATN, Landon MB, Spong CY, Lai Y, Leveno KJ, Varner MW, et al. Timing of elective repeat cesarean delivery at term and neonatal outcomes. N Engl J Med. 2009;360(2):111-120.

335. Morrison JJ, Rennie JM, Milton PJ. Neonatal respiratory morbidity and mode of delivery at term: influence of timing of elective caesarean section. Br J Obstet Gynaecol. 1995;102(2):101-106.

336. American College of Obstetricians and Gynecologists' Committee on Obstetric Practice, Society for Maternal-Fetal Medicine. Nonmedically indicated early-term deliveries. ACOG Committee Opinion No. 765. Obstet Gynecol. 2019;133(2):e156-e163.

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