Interpretation and comparison to current literature
MCDA twins are considered to be at highest risk of perinatal morbidity and mortality because of acute hemodynamic intrapartum changes mediated by placental vascular anastomoses[10]-[11]. However, due to a lack of evidence, there is no clear consensus regarding the optimal mode of delivery in uncomplicated twins. Despite the relevance of chorionicity, most studies addressing the contribution of the mode of delivery in perinatal morbidity have not been stratified accordingly. Furthermore, relevant aspects such as the mode of onset of labor or long-term neurodevelopment have not been taken into consideration.
To date, only eight studies have taken chorionicity into account when analyzing the optimal mode of delivery in uncomplicated twins, with disparate designs and neonatal morbidity criteria[16]-[23]. Of the eight studies, four were secondary analysis of previous studies. None of them considered the mode of onset of labor in the TOL group or long-term NDI. The most relevant data of each study are summarized in table 6. Our findings are consistent with those reported in the above-mentioned studies, demonstrating that attempted vaginal delivery for uncomplicated MCDA twins is a safe management option, when performed by a trained obstetric team, and has a low perinatal morbidity rate. Therefore, when first twin is in vertex presentation, PCS does not seem to be the strategy to avoid perinatal adverse events in uncomplicated MCDA pregnancies after 32.0 weeks, but rather shows a slight increase in them (aOR 1.36, 95% CI 0.24-7.81).
The gestational age at delivery in the pregnancies included in the different studies is highly variable, ranging from 24.0 to 38.6 weeks. In our study, we decided to include moderate to late preterm births (32.0 – 36.6 weeks) to avoid masking a protective effect of cesarean section in that range of gestational age.
The impact of the mode of delivery in twins on 2-year-neurodevelopment was studied by Asztalos et al. in 2016[26]. The authors performed a secondary analysis of the Twin Birth Study , a large randomized controlled trial designed to compare planned vaginal delivery and PCS[5]. This study finally included 2,323 pregnancies, of which 555 were MCDA. Although they do not stratify the data in relation to chorionicity, the authors conclude that a policy based in PCS provides no benefit to children at 2 years of age [5.99% vs. 5.83%, OR 1.04 (95% CI 0.77-1.41), p=0.79]. Our study yields similar results, although the NDI rate is slightly higher in PCS group compared to TOL and their different onset modalities (spontaneous or induced). However, the rate of 2-year-NDI is similar to that reported by other authors when a selective analysis of MCDA pregnancies is performed[27].