Results
(1) Development cohort
During the study period, a total of 1,356 twin pregnant women who met
the inclusion criteria and delivered at SNUH, were assigned as the
development cohort. The indications for IOL were maternal request
(n=517), prolonged pregnancy (n=484), suspected intrauterine growth
retardation (n=147), rupture of membrane (n=110), preeclampsia (n=60),
gestational diabetes (n=13), suspected large for gestational age fetus
(n=9), chronic hypertension (n=6), oligohydramnios (n=5) and other
reasons for maternal medical condition (n=5).
Of these twin pregnant women, 17.0%
(n=230) underwent cesarean delivery and 83.0% (n=1126) underwent
vaginal delivery. The reasons for cesarean delivery were failure to
progress (n=81), failed induction (n=64), maternal condition (such as
medical reason or request, n=54), and non-reassuring fetal status
(n=31). Failed induction was defined as failure to give birth after more
than three days of serial induction without rupture of the
membrane.23,24
Table 1 compares the clinical variables according to the final mode of
delivery. The gestational age at labor induction and presentation of the
second twin did not differ between the two groups. However, patients who
underwent cesarean delivery were older, had shorter height, higher
pregestational body mass index, less effaced and dilated cervix, and
heavier birth weight of twins. In addition, patients who underwent
cesarean delivery were more likely to become pregnant after assisted
reproductive techniques and had a higher frequency of nulliparous and
dichorionic twins.
To find the best prediction model for cesarean delivery with these
clinical variables, we conducted a three-fold CV with 100 repetitions.
The study population in the development cohort was randomly divided into
a training set and a test set with a ratio of 2:1, and the prediction
model was developed using logistic regression analysis in the training
set, and the AUROC was calculated in the test set. Table S1 shows the
mean AUROC for each prediction model. Among the possible models, the
prediction model including maternal age, parity, maternal height,
cervical effacement, and total birth weight of twins, had the highest
average AUROC value in the test set and was selected as the best
prediction model [AUROC, 0.742 (95% CI 0.700-0.785) in the training
set and 0.733 (95% CI, 0.671-0.794) in the test set]. Table 2
summarizes the odds ratios of each variable in the best prediction model
in the SNUH development cohort. In addition, a nomogram for predicting
the risk of cesarean delivery after IOL in twin pregnancy (Figure 1) and
a web-based predictive calculator (Figure 2) was developed.
(2) Validation cohort.
In SNUBH, a total of 347 twin pregnant women who met the inclusion
criteria and delivered between 2005 and 2018 were assigned as the
external validation cohort. In this validation cohort, 26.5% of women
(n=92) underwent cesarean delivery. External validation of the
prediction model for cesarean delivery derived from the SNUH cohort was
performed on this cohort. The AUROC in this cohort was 0.714 (95% CI,
0.650-0.777), which was similar to that of the development cohort
(Figure 3).