Prospective risk of late stillbirth in monochorionic twins: a regional cohort study.

OBJECTIVE: Monochorionic (MC) pregnancies are routinely delivered electively at late preterm gestation with the aim of avoiding stillbirth at term. The aim of this study was to evaluate the prospective risk of late stillbirth in a large regional cohort of twin pregnancies of known chorionicity.

METHODS: This was a retrospective study of all twin pregnancy births of known chorionicity between 2000 and 2009 from a large regional cohort consisting of nine hospitals. Prospective risk was calculated per 1000 fetuses rather than pregnancies, as each twin pregnancy had two gestations at risk of stillbirth.

RESULTS: A total of 3005 twin pregnancies delivered after 26 weeks' gestation in the Southwest Thames Obstetric Research Collaborative. The total risk of stillbirth after 26 weeks in MC twins (19.1 per 1000 fetuses) was significantly higher than in dichorionic (DC) twins (6.5 per 1000 fetuses), with an odds ratio (OR) of 2.97 (95% CI, 1.71-5.18). The risk of stillbirth in MC twins did not change significantly between 26 weeks (1.8 per 1000 fetuses) and 36 weeks (3.4 per 1000 fetuses), with an OR of 1.85 (95% CI, 0.3-13.2). The equivalent figures for DC twins were 0.6 per 1000 fetuses and 2.1 per 1000 fetuses, respectively (OR, 3.4 (95% CI, 0.9-13.2)).

CONCLUSIONS: The risk of stillbirth in MC twins does not appear to increase significantly near term. This may be due to a policy of routine surveillance and elective delivery from 36 weeks. The data do not support a policy of elective delivery before 36 weeks' gestation in MC pregnancies.