Zika and the Risk of Microcephaly

An analysis of data from Brazil reveals a strong association between the risk of microcephaly in a newborn and the risk of Zika virus infection during the mother's first trimester of pregnancy. The association in the second and third trimesters was negligible. Zika virus (ZIKV) infection during pregnancy has been linked to birth defects, 1 yet the magnitude of risk remains uncertain. Investigators studying the 2013–2014 Zika outbreak in French Polynesia estimated that the risk of microcephaly due to ZIKV infection in the first trimester of pregnancy was 0.95% (95% confidence interval, 0.34 to 1.91), on the basis of eight microcephaly cases identified retrospectively in a population of approximately 270,000 people with an estimated rate of ZIKV infection of 66%. 2 In the current outbreak, thousands of cases of infants with suspected microcephaly or other developmental anomalies of the central nervous system that may . . .