Early prediction of severe twin-to-twin transfusion syndrome.

This extended series of 303 monochorionic twin pregnancies examined at 10-14 weeks gestation explores the possible association of increased fetal nuchal translucency thickness (NT) in the early prediction of severe twin-to-twin transfusion syndrome (TTS). Of 303 pregnancies, there were 16 in which at least one fetus was structurally or chromosomally abnormal and in the remaining 287 ongoing pregnancies there were 43 (15%) which developed severe TTS. The median fetal NT was 1.0 multiples of the median (MOM) and NT was >95th centile in 47 (8.2%) fetuses and in at least one fetus in 37 (12.9%) pregnancies. The prevalence of increased NT in the pregnancies that developed TTS [17.4% (n = 15) of fetuses and 28% (n = 12) of pregnancies] was significantly higher than in the non-TTS group [6.6% (n = 32) and 10.2% (n = 25) respectively; Z: = -3.4, P: < 0.001 and Z: = 3.2, P: < 0.001 respectively], likelihood ratio of increased fetal NT for prediction of TTS = 3.5 [95% confidence interval (CI) 1.9-6.2]. In 153 of the pregnancies, an ultrasound examination was also performed at 15-17 weeks gestation and intertwin membrane folding was seen in 49 (32%) cases; 21 of these (43%) subsequently developed TTS compared to two (1.9%) of the 104 pregnancies without membrane folding (Z: = 6.6, P: < 0.001), likelihood ratio of membrane folding for prediction of TTS = 4.2 (95% CI 3.0-6.0).