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The optimal route of delivery for the twin gestation is not known. While vaginal delivery is common when both twins are vertex and of similar size, cesarean delivery is typically performed when the first twin is breech and in many cases when the first twin is vertex and the second is malpositioned. Cesarean delivery is resorted to in these cases out of concern for the morbidity that, in some, but not all studies has been associated with the second twin that includes birth trauma due to increased manipulation during delivery, cord prolapse, premature placental separation, and a prolonged second stage for the second twin as compared with the first. Most studies documenting an increased morbidity in the second twin are retrospective as randomized controlled trials are difficult to perform in this group of patients.1–7 Indeed, the only published randomized trial to date was small and did not show an increased morbidity of the second twin.8
The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal–Fetal Medicine Units Network (MFMU) network performed a 2-year prospective observational study of cesarean delivery and included twin gestations.9 Using data from this cesarean registry, we compared outcomes of the second twin when both twins delivered by cesarean to those where the first twin delivered vaginally and the second by cesarean. Our objective was to identify whether the second twin experienced increased short-term morbidity as part of a combined route of delivery.
MATERIALS AND METHODS
This is a secondary analysis of a prospective cohort study designed to assess several issues related to cesarean delivery. The study was performed by the NICHD MFMU Network, and details of the data collection and study design have been previously published.9 Briefly, between January 1, 1999, and December 31, 2000, all women undergoing a cesarean delivery at one of the 13 participating centers were prospectively ascertained. Each center’s institutional review board approved the study protocol. This secondary analysis was limited to laboring women to provide comparable groups for analysis as all combined twin deliveries experience labor while only a proportion of the pregnancies when both twins delivered by cesarean experience labor.
Maternal and neonatal outcomes were compared in those twin pregnancies in which the first twin was delivered vaginally and the second twin by cesarean to those pregnancies where both were delivered by cesarean. Maternal demographics, gestational age, and birth weight were compared, as well as labor characteristics in the two groups. Maternal complications were also examined. Comparison of neonatal outcomes in the two groups was limited to the second twin.
Continuous variables were compared using the Wilcoxon rank-sum test. Categorical variables were compared with the use of the χ2 or Fisher exact test, where appropriate. Logistic regression analysis was performed adjusting for differences in demographics and labor characteristics looking at infection outcomes in the mothers and infants. Unless otherwise noted, the response rate for the variables was 95% or greater. Nominal two-tailed P values are reported with statistical significance considered as a P value of <.05. No adjustment was made for multiple comparisons. Statistical analysis was performed with SAS (SAS Institute, Cary, NC).
There were 1,887 twin pregnancies in the cesarean registry, of which 1,028 experienced labor and are included in this analysis. Cesarean delivery of both twins occurred in a total of 849 pregnancies, and 179 (17%) delivered the first vaginally and underwent a cesarean delivery of the second twin. Table 1 shows demographic characteristics including gestational age and birth weight of the two groups. There were fewer nulliparous and more African-American women in the combined delivery group.
Labor characteristics are shown in Table 2. The combined group experienced more labor augmentation and a longer duration of rupture of membranes to delivery. The indication for cesarean delivery was different in the two groups (all P<.001) with the combined group being more likely to undergo cesarean delivery for a nonreassuring fetal heart rate tracing (37% compared with 13%), abnormal presentation (53% compared with 38%), and less likely to undergo cesarean delivery for labor dystocia (3% compared with 14%). Other indications for cesarean included abruption (1.5%), previa with hemorrhage (.3%), and presence of a herpetic lesion (less than 0.1%). In the combined group, 8.9% of the second twins had a failed operative vaginal delivery.
As shown in Table 3, endometritis was more common in the combined group. Chorioamnionitis and wound complications were similar in the two groups, as was the need for blood transfusion. Logistic regression analysis was performed adjusting for the impact of the indication for cesarean delivery, intrapartum antibiotic use, nulliparity, race, and the length of time of rupture of membranes to delivery on endometritis. After adjustment the odds ratio was 1.3 (95% confidence interval 0.7–2.2).
Table 4 shows neonatal outcomes in the two groups. Culture-proven neonatal sepsis was more common in the combined delivery group (P=.048). Serious neonatal sequelae including hypoxic ischemic encephalopathy, intraventricular hemorrhage grade III or IV, necrotizing enterocolitis, seizures, and death were similar in the two groups. Logistic regression analysis was performed looking at the impact of the indication for cesarean delivery, intrapartum antibiotic use, nulliparity, race, and the time from membrane rupture to delivery on culture proven neonatal sepsis. The relationship between neonatal sepsis and type of delivery was no longer significant after this adjustment (odds ratio 1.5, 95% confidence interval 0.7–3.3). To examine whether the condition of twin A impacted the condition of twin B, the following neonatal outcomes were compared: cord pH less than 7.0, a 5-minute Apgar score of 3 or less, confirmed seizure, and proven sepsis. There was no statistically significant difference between twin A and twin B in the incidence of these outcomes when compared individually or as part of a composite, all P>.05.
In this study of combined twin delivery, infectious morbidity was increased in those pregnancies in which the first twin underwent vaginal delivery and the second twin underwent a cesarean delivery as compared with those in which both twins delivered by cesarean. Endometritis was increased in the combined group from 9% to 13%, and neonatal sepsis was increased from 5% to 9% as compared with the group in which both twins delivered by cesarean. These findings were not significant, however, when the indication for cesarean delivery, the length of labor, the use of intrapartum antibiotics, and demographic differences were adjusted for. More serious morbidity or mortality to the second twin was not seen in the combined group, including poor condition at birth as determined by cord pH, Apgar score, neurologic injury including hypoxic ischemic encephalopathy, seizure, intraventricular hemorrhage, and death. Although these results suggest morbidity is increased in those twins for whom vaginal delivery of both is unsuccessful, this morbidity is limited to infection related to labor and the reason for the cesarean and does not appear to result in poor condition at birth or translate to adverse neurologic outcome.
The safety of vaginal delivery for twins has long been questioned due to concerns over increased morbidity and mortality in the second twin. Most of the studies performed to date are retrospective in design due to the difficulties of performing a randomized trial on route of delivery. These studies have provided conflicting information on the safety of vaginal delivery of twins. Hogle et al4 performed a systematic review and meta-analysis to pool the existing data and determine whether a policy of planned cesarean for twins improves neonatal outcomes. They identified 67 articles but were able to include one four due to methodologic limitations of the other 63. Three of the four studies included were not randomized. In the 1,932 infants reported on in the resulting meta-analyses, no increased morbidity or mortality was seen in the twins who underwent vaginal delivery. Sheay et al6 showed increased perinatal mortality of the second twin in a cohort of 293,788 fetuses identified through data assembled by the National Center for Health Statistics and the CDC. This morbidity was limited to stillbirths, that is, the risk of neonatal mortality excluding stillbirths was not increased in the second twin regardless of the route of delivery. A recent retrospective study of 1,377 births in England, North Ireland, and Wales found different results than these prior studies.5 Although there was no association between birth order and risk of death overall, there was when the analysis was limited to term births. The risk of death was increased in those twins undergoing vaginal compared with cesarean delivery. The accompanying editorial suggested that the clinician balance the potential for increased neonatal mortality with the increased risks to the mother of cesarean delivery. They pointed to the importance of completing a randomized trial(s) before recommending routine cesarean delivery for all twins.10 To date, there has been one published randomized trial of the route of delivery in twin gestations. This trial was small, enrolling only 54 twins, 27 of which received a cesarean delivery and 27 of which underwent a vaginal delivery. No difference was seen in neonatal outcomes; however, maternal morbidity was greater in the cesarean group due to infection. Our study is consistent with these findings.
The MFMU Cesarean Registry afforded us the opportunity to look at a specific aspect of twin delivery involving the second twin, that is, what increased risk if any does the second twin face if an attempt at vaginal delivery results in a combined delivery. We expected that the second twin of a combined delivery may be at particular risk of adverse outcome. Our findings show that combined twin delivery is associated with an increased risk of infection. This appears to be secondary to an increased time in labor, the indication for cesarean, and possibly the vaginal manipulation that occurs with failed vaginal delivery of the second twin, something not addressed in our study. We are reassured that we did not find more serious adverse outcomes including death of the second twin. In the absence of more definitive data, our study suggests that an attempt at vaginal delivery should not be avoided due to the fear of an unexpected cesarean delivery of the second twin.
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