Weight discordance and perinatal mortality in twins: analysis of the Southwest Thames Obstetric Research Collaborative (STORK) multiple pregnancy cohort.

OBJECTIVES The degree of actual intertwin birth weight (BW) or ultrasound estimated fetal weight (EFW) discordance that justifies elective delivery is yet to be established. The main aim of this study was to ascertain the performance of BW and ultrasound EFW discordance in the prediction of perinatal loss in twin pregnancies. METHODS This was a retrospective study of all twin pregnancy births from a large regional cohort of nine hospitals over a 10-year period. Intertwin BW and ultrasound EFW discordance were analyzed in relation to the occurrence of stillbirth or neonatal death of one or both twins from 26 weeks' gestation as obtained from a mandatory national register. Receiver-operating characteristics (ROC), survival and logistic regression analyses were performed to evaluate the contribution of weight discordance in determining perinatal loss. RESULTS A total of 2161 twin pregnancies were included in the analysis. The area under the ROC curve for the prediction of perinatal loss was similar for BW and ultrasound EFW discordance (P = 0.62). Kaplan-Meier analysis showed that twins with BW or EFW of ≥ 25% discordance had a significantly lower survival trend than did those with lesser degrees of discordance (P < 0.001). The hazard ratios for the risk of total perinatal loss in twins with a BW or EFW discordance of ≥ 25% were 7.29 (95% CI, 4.37-12.00) and 7.28 (95% CI, 4.46-11.92), respectively. Logistic regression analysis demonstrated that BW discordance and gestational age, but not chorionicity or individual fetal size percentile, were independently associated with perinatal mortality. CONCLUSIONS An EFW discordance of ≥ 25% represents the optimal cut-off for the prediction of stillbirth and neonatal mortality irrespective of chorionicity or individual fetal size. A policy of increased fetal surveillance commencing from 26 weeks' gestation might be reasonable for pregnancies beyond this cut-off, but this would require confirmation in large-scale prospective trials.