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

Objective Single intrauterine death (sIUD) in twin pregnancy is associated with a significant risk of cotwin demise and preterm birth (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 diagnosis of sIUD. Methods This was a cohort study of all twin pregnancies booked for antenatal care in a large regional network of nine hospitals over a 10-year period. Ultrasound data were matched to hospital delivery records and to a mandatory national register for stillbirth and neonatal loss provided by the Centre for Maternal and Child Enquires. Cases with double fetal loss at the time of the scan and cases of sIUD occurring at or after 34weeks of gestation were not included in the analysis. The relative risk (RR) of PTB at <34, <32 and <28 weeks of gestation in twin pregnancies complicated by sIUD was assessed and compared with that in twin pregnancies without fetal loss. The risk of PTB at <34 weeks was stratified according to the gestational age at diagnosis of sIUD. The risk of PTB in twin pregnancy after sIUD according to the gestational age at death was also explored. Results The analysis included 3013 twin gestations (2469 dichorionic (DC) and 544 MC). Median gestational age at birth was lower in the pregnancies complicated by sIUD compared with those thatwere not (32.0weeks: interquartile range (IQR), 29.0–34.3weeks vs 36.7weeks: IQR, 35.0–37.6; P<0.001) and this difference persisted when stratifying the data according to chorionicity (P<0.0001 for both MC and DC pregnancies). The risk of PTB at <34 weeks (RR, 4.3 (95% CI, 3.5–5.2)), <32 weeks (RR, 6.1 (95% CI, 4.6–8.1)) and <28 weeks (RR, 12.4 (95% CI, 6.9–22.2)) of gestation was higher in pregnancies complicated by sIUD compared with those which did not experience fetal loss. This association was observed both inMC andDCtwin gestations.When comparedwith DC pregnancies, MC twins affected by sIUD were not at significantly increased risk of PTB before either 34, 32 or 28 weeks of gestation. The risk of PTB at <34 weeks of gestation was higher when the sIUD occurred at a later gestational age (chi-square test for trend, P<0.001). Conclusions Twin pregnancies complicated by sIUD, regardless of the chorionicity, have a significantly higher risk of PTB at <34, <32 and <28 weeks of gestation. The risk of PTB at <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.