The influence of chorionicity and gestational age at single fetal loss on the risk of preterm birth in twin pregnancies: analysis of the STORK multiple pregnancy cohort

Abstract

BACKGROUND: Single intrauterine death (sIUD) in twin pregnancies is associated with a significant risk of co-twin demise and pretermbirth (PTB), especially in monochorionic (MC) twins. However, it is yet to be established whether the gestational age at loss may influence the pregnancy outcome. The aim of this study was to explore the risk of PTB according to the gestational age at the diagnosis of sIUD. METHODS: A cohort study of all twin pregnancies from a large regional network of 9 hospitals over a ten-year period. Ultrasound data was matched to hospital delivery records and a mandatory national register for perinatal losses (CMACE). Cases with double fetal loss at the time of the scan were not included in the analysis. The cumulative rates of PTB before 34, 32 and 28 weeks of gestation was assessed in pregnancies which did vs those which did not experience sIUD. The risk of PTB was stratified according to the gestationalage at the diagnosis of sIUD. RESULTS: The analysis included 3013 twin gestations (2469 DC and 544 MC) . Median gestational age at birth was lower in the pregnancies complicated by sIUD compared to those which were not (32.0 weeks, IQR 29.0-34.3 vs 36.7 weeks, IQR 35.0-37.6; p < 0.001) and this difference persisted when stratifying the analysis according to chorionicity (p < 0.0001 for both MC and DC pregnancies). The risk of PTB before 34 weeks (RR: 4.3, 95% CI 3.5-5.2), before 32 weeks (RR: 6.1, 95% CI 4.6-8.1) and before 28 weeks (RR: 12.40, 95% CI 6.9-22.2) was higher in pregnancies complicated by a sIUD compared to those which did not experience any fetal loss. This association was observed both in MC and DC twin gestations. When compared to DC pregnancies, MC twins affected by sIUD were not at significantly increased risk of PTB either before 34, 32 or 28 weeks of gestation. The risk of PTB before 34 weeks of gestation was higher when the sIUD occurred at a later gestational age (Chi-square test for trend, p < 0.001). CONCLUSION: Twin pregnancies complicated by sIUD, regardless of the chorionicity, have a significantly higher risk of PTB before 34, 32 and 28 weeks of gestation. The risk of PTB before 34 weeks of gestation was higher when the sIUD occurred in the second half of the pregnancy. Large prospective multicenter studies with shared protocols for prenatal management are needed to ascertain the actual risk of spontaneous PTB in twin pregnancies affected by sIUD.