Discordant Zika Virus Findings in Twin Pregnancies Complicated by Antenatal Zika Virus Exposure: A Prospective Cohort.

BACKGROUND: There are limited data on the natural history of antenatal Zika virus (ZIKV) exposure in twin pregnancies, especially regarding intertwin concordance of prenatal, placental, and infant outcomes. METHODS: This prospective cohort study included twin pregnancies referred to a single institution from September 2015 to June 2016 with maternal ZIKV. Polymerase chain reaction (PCR) testing of maternal, placental, and neonatal samples was performed. Prenatal ultrasounds were completed for each twin, and histomorphologic analysis was performed for each placenta. Abnormal neonatal outcome was defined as abnormal exam and/or abnormal imaging. Two- to three-year follow-up of infants included physical exams, neuroimaging, and Bayley-III developmental assessment. RESULTS: Among 244 pregnancies, 4 twin gestations without coinfection were identified. Zika virus infection occurred at 16-33 weeks gestation. Zika virus PCR testing revealed discordance between dichorionic twins, between placentas in a dichorionic pair, between portions of a monochorionic placenta, and between a neonate and its associated placenta. Of the 8 infants, 3 (38%) had an abnormal neonatal outcome. Of 6 infants with long-term follow-up, 3 (50%) have demonstrated ZIKV-related abnormalities. CONCLUSIONS: Neonatal PCR testing, placental findings, and infant outcomes can be discordant between co-twins with antenatal ZIKV exposure. These findings demonstrate that each twin should be evaluated independently for vertical transmission.