Preterm birth or small for gestational age in a singleton pregnancy and risk of recurrence in a subsequent twin pregnancy.

OBJECTIVE To evaluate whether a history of preterm birth or small for gestational age (SGA) in a singleton pregnancy is associated with an increased risk of recurrence of the same condition in a subsequent twin pregnancy. METHODS Retrospective cohort study of twin pregnancies delivered in one maternal-fetal medicine practice from 2005 to 2014. Patients with a history of singleton preterm birth at less than 37 weeks of gestation were compared with patients with a history of singleton term birth and nulliparous patients. A similar analysis was performed for a history of SGA (birth weight less than 10%). RESULTS Six hundred forty-seven twin pregnancies were included. The prior singleton gestational age at delivery was significantly positively correlated with the twin gestational age at delivery (P<.001), and the prior singleton birth weight was significantly positively correlated with the birth weight of the larger twin (P<.001) and the smaller twin (P<.001). The rate of twin preterm birth before 32 weeks of gestation was 3.5% in patients with a prior term birth, 9.2% in nulliparous patients, and 26% in patients with a prior preterm birth (P<.001). The rate of SGA in patients with a prior birth not complicated by SGA was 42.1%, in nulliparous women it was 54.4%, and in patients with a history of SGA it was 65.2% (P=.007). On regression analysis, prior preterm birth and SGA of a singleton pregnancy were independently associated with recurrence of the same condition in a subsequent twin pregnancy. CONCLUSION Prior preterm birth and SGA in a singleton pregnancy increase the risk of the same condition in a subsequent twin pregnancy. We postulate that the extrinsic mechanism responsible for the pathophysiology of adverse outcomes in twin pregnancies overlaps with that in singleton pregnancies.