Objective
The purpose of this study was to estimate independent risk factors for cesarean delivery in patients with twin pregnancies who attempt vaginal delivery.
Study Design
This was an historic cohort of twin pregnancies that were delivered in 1 practice from June 2005 to February 2014. Baseline characteristics were compared between women who delivered vaginally and women who underwent cesarean delivery in labor. Logistic regression analysis was performed to estimate independent risk factors for cesarean delivery.
Results
Two hundred eighty-six women with twin pregnancies who had attempted vaginal delivery were included in the study. The overall modes of delivery were vaginal delivery (82.2%), cesarean delivery (17.8%), and combined vaginal-cesarean delivery (0%). The most common indication for cesarean delivery in labor was an arrest disorder (82.4%). The risk factors that were associated independently with cesarean delivery were nulliparity (adjusted odds ratio, 5.78; 95% confidence interval, 2.24–14.88) and advanced maternal age of ≥35 years (adjusted odds ratio, 2.36; 95% confidence interval, 1.16–4.80). The patients at highest risk for cesarean delivery (nulliparous, advanced maternal age, induced labor) still had a 48.6% likelihood of vaginal delivery.
Conclusion
In patients with twin pregnancies who attempt labor, nulliparity and advanced maternal age are associated independently with cesarean delivery in labor. However, even the patients at highest risk for cesarean delivery have nearly a 50% likelihood of successful vaginal delivery and therefore should be allowed to attempt vaginal delivery if it is desired and not otherwise contraindicated.
Twins now represent 3.3% of all live births in the United States. The majority of twins are born by cesarean delivery, and this rate has been increasing. In the United States, the rate of cesarean delivery of women with twin pregnancies rose from 53% in 1995 to 75% in 2008. This increase was seen both in vertex and breech twins; after adjustment for several risk factors, there was an approximate increase in cesarean delivery rate of 5% per year.
The safety of vaginal delivery of twins was suggested by several large observational studies and recently was established in a large, prospective, randomized trial. In that trial of 1398 women (2795 fetuses), the overall outcome of fetal or neonatal death or serious neonatal morbidity did not differ between women in the planned-cesarean-delivery group and women in the planned-vaginal-delivery group. Based primarily on the results of this study, a recent consensus statement by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine stated that women with twin pregnancies and a cephalic-presenting twin should be counseled to attempt vaginal delivery and that it is important to train residents to perform vaginal delivery of twins.
However, when counseling women with twin pregnancies about mode of delivery, it is important to discuss not only the safety of vaginal delivery but also the likelihood of a successful vaginal delivery for those who attempt it. In a recent large series of twins in Ireland, a trial of labor was attempted in 441 twin pregnancies and was successful in 338 (77%). In that series, vaginal breech extraction of the second twin was performed in 29% of those who delivered vaginally, and 4% of patients had a combined vaginal-cesarean delivery. On univariate analysis, they found that the risk factors for cesarean delivery in labor were nulliparity and assisted conception. However, this analysis did not control for other variables. We published our own experience of twin deliveries using active management of the second stage. Among 130 women who attempted vaginal delivery, 84.6% were successful; vaginal breech extraction of the second twin was performed in 77% of those who delivered vaginally, and there were no combined vaginal-cesarean deliveries. We found on univariate analysis that older maternal age and nulliparity were associated with cesarean delivery. Because there are many confounding risk factors in twin pregnancies (for example maternal age and assisted reproduction or maternal weight and gestational diabetes mellitus), it is important when analyzing risk factors for cesarean delivery that the statistical methods that are used are able to control for these confounders and to estimate independent risk factors for cesarean delivery.
The objective of this study was to use regression analysis to estimate independent risk factors for cesarean delivery in a large single-center cohort of women in the United States with twin pregnancies who attempt vaginal delivery. Using these data, obstetricians and patients with twin pregnancies could better understand the risk of cesarean delivery in labor and make an informed decision about mode of delivery.
Methods
After Biomedical Research Alliance of New York Institutional Review Board approval was obtained, the charts of all patients with twin pregnancies at ≥24 weeks of gestation who were delivered by a single maternal-fetal medicine practice from June 2005 (when our electronic medical record was established) to February 2014 were reviewed. We excluded patients who did not attempt vaginal delivery and patients for whom one or both of the twins were not alive in labor. Baseline characteristics and pregnancy outcomes were obtained from our computerized medical record. This analysis includes data from 130 patients in our original report of twin deliveries who attempted labor and from all of our patients with twin pregnancies who attempted labor subsequent to that publication.
All patients were delivered in a tertiary-care academic medical center with a level III neonatal intensive care nursery and 24-hour in-house pediatric and obstetric anesthesia availability. All patients’ labors were managed and deliveries performed by one of the attending obstetricians in our practice, with house staff involvement in all cases. Our protocols for management of labor and induction of labor in twin pregnancies have been described previously. In short, contraindications to vaginal twin delivery of twins in our practice are nonvertex-presenting twin, nonvertex second twin with an estimated fetal weight >20% larger than the presenting twin, nonvertex second twin with an estimated fetal weight <1500 g, and other usual contraindications to labor (eg, placenta previa, previous classical cesarean delivery). Patients with twin pregnancies have regional anesthesia in labor and continuous fetal heart rate monitoring of both twins. Oxytocin and amniotomy are used for standard indications. All twin deliveries occur in the operating room. Operative delivery of twin A is performed for the usual indications. If twin B is vertex and engaged, the patient is instructed to push, and amniotomy is performed. If twin B is breech or transverse, complete breech extraction is performed with standard obstetric maneuvers. If twin B is cephalic and unengaged, internal version is performed followed by breech extraction, as described previously. In our practice, we deliver all uncomplicated dichorionic twin pregnancies at 38 weeks of gestation and all uncomplicated monochorionic twin pregnancies at 37 weeks of gestation.
Using χ 2 analysis, we compared baseline characteristics between women who delivered vaginally and women who underwent cesarean delivery in labor. Baseline characteristics that were examined were advanced maternal age (AMA, age ≥35 weeks of gestation at time of delivery), chorionicity, in vitro fertilization (IVF), multifetal reduction, maternal race, nulliparity, any previous cesarean delivery, prepregnancy obesity (body mass index, ≥30 mg/kg 2 ), term delivery (≥37 weeks of gestation), induction of labor, premature rupture of membranes, gestational diabetes mellitus, and preeclampsia. A planned logistic regression was then performed that included only those variables that were significant (probability value, ≤ .05) on univariate χ 2 analysis; adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated to estimate those risk factors that were associated independently with cesarean delivery (IBM SPSS for Windows version 22.0; IBM Corporation, Armonk, NY). We then calculated the likelihood of vaginal delivery in 8 cohorts of patients, based on all the possible combinations of the presence or absence of the 3 most significant risk factors for cesarean delivery to estimate whether there is any cohort of women with twin pregnancies for whom a vaginal delivery is so unlikely it may not be worth attempting.
With the assumption of a 15% likelihood of cesarean delivery, an alpha error of 5%, and a power of 80%, approximately 280 total patients would be needed to show an absolute difference of 20% in any risk factor between patients who had a cesarean delivery and patients who had a vaginal delivery (for example, from 20% in the vaginal delivery group to 40% in the cesarean delivery group).
Results
Over the course of the study period, there were 663 women with twin pregnancies and live births at ≥24 weeks of gestation who were delivered by our practice. Of these, 286 women (43.1%) who attempted vaginal delivery comprised the study group. Of the 377 patients who did not attempt labor, only 17 patients (4.5%) had an elective cesarean delivery for no indication other than twin pregnancy. The baseline characteristics and delivery outcomes of the 286 patients in the study group are described in Table 1 . The overall modes of delivery were vaginal delivery (82.2%), cesarean delivery (17.8%), and combined vaginal-cesarean delivery (0%). The most likely indication for cesarean delivery in labor was an arrest disorder (82.4%). Among women who delivered vaginally, 74.9% had breech extraction of the second twin.
| Variable | Measure |
|---|---|
| Maternal characteristics (n = 286) | |
| Age, y a | 32.7 ± 6.2 |
| Prepregnancy body mass index, kg/m 2 a | 23.1 ± 4.2 |
| Gestational age at delivery, wk a | 36.5 ± 1.8 |
| Gestational age grouping, n (%) | |
| 24-27 6/7 wk | 2 (0.7) |
| 28-31 6/7 wk | 2 (0.7) |
| 32-35 6/7 wk | 68 (23.8) |
| ≥36 wk | 214 (74.8) |
| Birthweight, g a | |
| Twin A | 2516 ± 429 |
| Twin B | 2457 ± 437 |
| Delivery outcomes (n = 286) | |
| Mode of delivery, n (%) | |
| Vaginal-vaginal | 235 (82.2) |
| Cesarean-cesarean | 51 (17.8) |
| Vaginal-cesarean | 0 |
| Indication for cesarean delivery, n/N (%) | |
| Arrest disorder | 42/51 (82.4) |
| Nonreassuring fetal heart rate | 8/51 (15.7) |
| Cord prolapse | 1/51 (2.0) |
| Breech extraction of second twin (among vaginal deliveries), n/N (%) | 176/235 (74.9) |
| Operative delivery, n/N (%) | |
| Twin A | 25/286 (8.7) |
| Twin B | 10/286 (3.5) |
We estimated the association between maternal risk factors and cesarean delivery; the results are shown in Table 2 . On univariate analysis, the risk factors significantly associated with an increased likelihood of cesarean delivery were AMA, IVF, nonwhite race, nulliparity, term delivery, induction of labor, and gestational diabetes mellitus. These risk factors were included in a binary logistic regression analysis to estimate the risk factors independently associated with cesarean delivery ( Table 3 ). Nulliparity (aOR, 5.78; 95% CI, 2.24–14.88) and AMA (aOR, 2.36; 95% CI, 1.16–4.80) were the only risk factors independently associated with an increased risk of cesarean delivery. Induction of labor, which had one of the strongest associations with cesarean delivery on univariate analysis, still had a trend towards a positive association with cesarean delivery on regression analysis ( P = .08), but the 95% CI crossed 1.0, so the association was not statistically significant (aOR, 2.10; 95% CI, 0.96–4.57).
| Variable | Cesarean delivery (n = 51), % | Successful vaginal delivery (n = 235), % | P value a |
|---|---|---|---|
| Advanced maternal age (≥35 y) | 56.9 | 31.5 | .001 |
| Monochorionic | 13.7 | 13.6 | .984 |
| In vitro fertilization | 76.5 | 53.6 | .003 |
| Multifetal reduction | 7.8 | 4.3 | .282 |
| Nonwhite race | 21.6 | 8.5 | .007 |
| Nulliparity | 88.2 | 53.6 | < .001 |
| Previous cesarean delivery | 7.8 | 4.7 | .367 |
| Prepregnancy obesity | 3.9 | 6.5 | .485 |
| Term delivery (≥37 wk) | 68.6 | 46.8 | .005 |
| Induction of labor | 68.6 | 41.3 | < .001 |
| Premature rupture of membranes | 13.7 | 13.6 | .984 |
| Gestational diabetes mellitus | 17.6 | 6.9 | .014 |
| Preeclampsia | 10.0 | 9.8 | .971 |
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