Because of assisted reproductive technologies, twin pregnancy occurs more frequently now than in the past, and it complicates 2 to 3% of all births.1,2 Twins are at higher risk for an adverse perinatal outcome than singletons.3,4 Planned cesarean section, as compared with planned vaginal delivery, may reduce this risk.5 Although a small, randomized, controlled trial did not show better perinatal outcomes with planned cesarean section than with planned vaginal delivery,6 several cohort studies have shown a reduced risk of adverse perinatal outcomes for both twins, or for the second twin, when twins at or near term were delivered by means of elective cesarean section.7-10 Despite the lack of evidence to support a policy of planned cesarean section for twins at or near term, the rates of elective cesarean section for twins have increased in North America and worldwide. 11,12
We conducted the Twin Birth Study to compare the risk of fetal or neonatal death or serious neonatal morbidity with two delivery strategies — planned cesarean delivery or planned vaginal delivery with cesarean delivery only if indicated — for twin pregnancies between 32 weeks 0 days and 38 weeks 6 days of gestation, if the leading twin was in the cephalic presentation.
METHODS
Study Design
Women were eligible for the study if they had a twin pregnancy between 32 weeks 0 days and 38 weeks 6 days of gestation, the first twin was in the cephalic presentation, and both fetuses were alive with an estimated weight between 1500 g and 4000 g, confirmed by means of ultrasonography within 7 days before randomization. We enrolled women with pregnancies as early as 32 weeks of gestation because many women with twins wish to begin planning the method of delivery at this time and because many twin births are preterm.
Exclusion criteria were monoamniotic twins, fetal reduction at 13 or more weeks of gestation, lethal fetal anomaly, contraindication to labor or vaginal delivery (e.g., fetal compromise, first twin substantially larger than the second twin, fetal anomaly or condition that might cause mechanical problems at delivery, and previous vertical uterine incision or more than one previous low-segment cesarean delivery), and previous participation in the Twin Birth Study.
Study Oversight
The research ethics committee at each participating center approved the study protocol, which is available with the full text of this article at NEJM.org. The first, second, and last authors take responsibility for the accuracy and completeness of the reported data and for the fidelity of the report to the study protocol. All the women provided written informed consent before being enrolled.
Treatment Protocol
Women were randomly assigned to planned cesarean section or planned vaginal delivery. Randomization was centrally controlled at the Centre for Mother, Infant, and Child Research at Sunnybrook Health Sciences Centre in Toronto with the use of a computerized randomization program stratified according to parity (0 vs. ≥1) and gestational age (32 weeks 0 days to 33 weeks 6 days, 34 weeks 0 days to 36 weeks 6 days, or 37 weeks 0 days to 38 weeks 6 days), with the use of random block sizes.
Data were abstracted from the medical records at participating centers by trained study staff and were recorded, after delivery, on standardized data-collection forms. Participating centers assessed fetal growth and well-being with the use of ultrasonography at least every 4 weeks and with the use of nonstress or biophysical profile tests twice weekly if needed; were prepared to perform a cesarean section within 30 minutes if necessary; and had anesthetic, obstetrical, and nursing staff available in the hospital at the time of planned vaginal delivery.
Elective delivery by means of either cesarean section (for women in the planned-cesarean group) or labor induction (for women in the planned-vaginal-delivery group) was planned between 37 weeks 5 days and 38 weeks 6 days of gestation,