Contribution of twin-to-twin transfusion syndrome to preterm birth among monochorionic biamniotic and bichorionic biamniotic twin pregnancies

AIMS: To determine the contribution of twin-to-twin transfusion syndrome (TTTS) to preterm birth (PTB) at <37 weeks of gestation among Japanese twin pregnancies. METHODS: An observational study using 3241 MC-BA (monochorionic biamniotic) and 6581 BC (bichorionic biamniotic) twin pregnancies. We focused on TTTS, preterm premature rupture of membranes (PPROM), pregnancy-induced hypertension (PIH), and fetal sex as possible causes of PTB. RESULTS: PTB was more common in MC-BA than in BC twin pregnancies (66.9% vs. 57.6%, P<0.0001) whereas PTB after PPROM (8.0% vs. 10.0%) and PIH (5.7% vs. 5.9%) was not. PTB after TTTS occurred in 7.3% of women with MC-BA twins. PTB was significantly more common for male-male pairs than for female-female pairs among both MC-BA (69.2% vs. 64.7%) and BC (59.6% vs. 56.3%) twins. CONCLUSION: The elevated risk of PTB among MC-BA twins could be explained by the occurrence of TTTS.