Uncomplicated Monochorionic Diamniotic Twins and the Timing of Delivery

I n the past 20 years, advancing maternal age and greater reliance on assisted-conception techniques have dramatically increased the incidence of multiple births, including monochorionic twins (see Glossary) [1,2]. Concomitantly, there have been advances in our understanding of these high-risk pregnancies. The offspring of multiple pregnancies are at greater risk for adverse perinatal outcomes compared to their singleton counterparts, predominantly due to increased risks for preterm delivery and due to monochorionicity [3]. The link between monochorionicity and adverse perinatal outcomes has become increasingly strong [4]. Monochorionic pregnancies have an approximately 15% risk of developing the twin-to-twin transfusion syndrome (TTTS), which can be associated with perinatal mortality and morbidity despite treatment [5]. In addition, single intrauterine fetal demise (IUFD) in a monochorionic pregnancy may be associated with a more-than 20% risk for multicystic encephalomalacia in the surviving co-twin [6]. Despite these advances in knowledge about risks, there is very little consensus about the management of these high-risk pregnancies. In addition, there is the temptation to be reassured by increasing gestational age as the potential complications of prematurity recede. Recent studies suggest, however, that the offspring of a multiple gestation may benefi t from delivering prior to their expected date of delivery [7,8]. Several studies have focused on the " prospective risk of fetal death " to help determine by which gestational age a multiple pregnancy should be delivered [7,8]. For twins, the prospective risk of fetal death appears to be equivalent to that of post-term singletons at approximately 37 to 38 weeks' gestation [7,8]. The prospective risk of fetal death for twins intersects with neonatal death at approximately 39 weeks' gestation, indicating that it may be reasonable to consider delivery of uncomplicated twins prior to 40 weeks' gestation [8]. These studies, however, did not address the impact of chorionicity on the decision to deliver a multiple pregnancy. In this issue of PLoS Medicine, Barigye et al. report the prospective risk of fetal death in uncomplicated monochorionic diamniotic twin pregnancies derived from a cohort of pregnancies that were managed at a single tertiary care referral center and that delivered after 24 weeks' gestation [9]. Patients were excluded from the study if the pregnancy was complicated by TTTS, monoamnionicity, intrauterine growth restriction, growth discordance, structural anomalies, or twin reversed arterial perfusion sequence. Conjoined twins and high-order multiples were also excluded. All patients with uncomplicated monochorionic twins were managed according to a standard protocol. …