Among mothers infected with Zika virus in the South American French territories, birth defects were found in 7% of fetuses and infants, according to research published in the New England Journal of Medicine. Defects occurred more frequently in fetuses and infants whose mothers had been infected early in pregnancy.
Between March and November 2016, symptomatic mothers in whom Zika virus infection was confirmed by polymerase chain reaction were enrolled in a prospective cohort study (ClinicalTrials.gov identifier: NCT02916732).
Of the 555 fetuses and infants included in the analysis, 5.0% were not carried to term or were stillborn. Neurologic and ocular defects often associated with Zika virus infection occurred in 7.0% (95% CI, 5.0-9.5) of fetuses and infants; 10 were not carried to term for medical reasons and 1 was stillborn.
Microcephaly occurred in 5.8% of fetuses and infants and was deemed severe in 1.6% of cases. The reported defects were also more common when Zika virus infection occurred during the first trimester (12.7%) than when infection occurred in the second or third trimesters (3.6% and 5.3%, respectively; P =.001).
The overall rates of Zika virus-associated birth defects reported in this study are similar to those reported in the United States and US territories but much lower than the 42% observed in a Brazilian cohort. This is not attributable to the numbers of microcephaly cases but rather to cases of wider neurologic defects. The differences may be partially explained by the number of pregnancies terminated for medical reasons in this cohort.
The rates of defects may possibly have been higher if asymptomatic infections were included, as recent studies showed no association between viral load and risk. Further long-term studies will be necessary to determine late-onset manifestations of defects not detected at birth.
Hoen B, Schaub B, Funk AL, et al. Pregnancy outcomes after ZIKV infection in French territories in the Americas. N Engl J Med. 2018;378:985-994.