Stillbirth and Neonatal Mortality in Monochorionic and Dichorionic Twins: A Population-Based Study EDITORIAL COMMENT

It is well established that twins have a higher risk of adverse birth outcomes compared with singletons; the stillbirth rate and neonatal mortality among twins are at least 4 times higher in twins. Chorionicity is an important predictor of perinatal mortality in twins. Most studies have reported higher risks of adverse perinatal outcomes in monochorionic (MC) twins compared with dichorionic (DC) twins. No large population-based studies have examined the prospective risk of stillbirth by gestational age for twin pregnancies, especially with stratification by chorionicity. The primary aim of this population-based study was to compare stillbirth and neonatal mortality in DC and MC twins by cause of death and over time. A secondary aim was to quantify the prospective risk of stillbirth in MC and DC twins by gestational age. Data on twin pregnancies delivered between 1998 and 2007 were obtained from the Northern Survey of Twin and Multiple Pregnancy, which registers all multiple pregnancies in the north of England. The prospective gestational age-specific risk of stillbirth was calculated using number of stillborn fetuses at or beyond a given gestational period per 1000 fetuses in continuing pregnancies. A total of 4565 twin maternities (9130 twins) were examined; the overall twinning rate was 14.9 per 1000 maternities. During the 10-year study period, the overall perinatal mortality rate was 40.0 per 1000 twins; this included stillbirth and neonatal mortality rates of 18.0 and 23.0 per 1000 live births, respectively. Compared with DC twins, the stillbirth rate in MC twins was 3.6 fold higher (44.4 vs. 12.2 per 1000 births) and the neonatal mortality rate was 1.5 fold higher (32.4 vs. 21.4 per 1000 live births); the relative risk was 3.6, with a 95% confidence interval of 2.6 to 5.1, and was 1.5, with a 95% confidence interval of 1.04 to 2.2, respectively. No significant improvement over time occurred in either group with regard to stillbirth or neonatal mortality rate. The prospective risk of antepartum stillbirth at all gestational ages in MC twins was significantly higher than DC twins; the highest risk was before 28 completed weeks of gestation. These findings demonstrate higher rates of stillbirth and neonatal mortality for MC twins compared with DC twins, with no improvement in either group during the 10-year study period. The prospective risk of antepartum stillbirth is much higher in MC than DC twins at all gestational ages.