Study design
(1) Development cohort
In this retrospective cohort study,
this group consisted of twin pregnant women underwent IOL at ≥ 36 weeks
of gestation at SNUH from 2005 to 2018. Twin pregnant women with the
following inclusion criteria were included: 1) both viable fetuses; 2)
the first baby in the cephalic presentation; 3) no contraindication for
IOL (e.g., abnormal placentation, fetal compromise, fetal congenital
anomaly, previous uterine surgery, or cesarean delivery); and 4) absence
of spontaneous labor, which is defined as regular uterine contractions
with cervical change. Women who gave birth through combined delivery
(cesarean delivery of the second baby followed by vaginal delivery of
the first baby) were excluded.
(2) Validation cohort.
In this validation cohort, the study population consisted of twin
pregnant women who underwent IOL at ≥ 36 weeks of gestation at SNUBH
from 2005 to 2018. In SNUBH, it is routine practice to perform IOL only
in cases with the cephalic presentation of both fetuses, therefore twin
pregnancies with cephalic (1st baby) / non-cephalic (2nd baby)
presentation are not candidates for IOL.
We collected clinical characteristics
including maternal age, maternal height, maternal weight, pregestational
body mass index (BMI, divided by weight in kilograms (kg) by the square
of their height in meters (m2)), parity, gestational
age at IOL, gestational age at delivery, method of conception, cervical
examination, chorionicity, presentation, and birth weight of each twin,
and summated birth weight of both twins. The variables were compared
between pregnant women who had a successful vaginal delivery and those
who underwent cesarean delivery after IOL. This retrospective study was
approved by the Institutional Review Board of SNUH and SNUBH.