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Original Investigation
January 3, 2017

Birth Defects Among Fetuses and Infants of US Women With Evidence of Possible Zika Virus Infection During Pregnancy

Author Affiliations
  • 1Centers for Disease Control and Prevention, Atlanta, Georgia
  • 2New York City Department of Health and Mental Hygiene, Queens, New York
  • 3Massachusetts Department of Public Health, Boston
  • 4New York State Department of Health, Albany
  • 5Virginia Department of Health, Richmond
  • 6Texas Department of State Health Services, Austin
  • 7Florida Department of Health, Tallahassee
JAMA. 2017;317(1):59-68. doi:10.1001/jama.2016.19006
Key Points

Question  What proportion of fetuses and infants of women in the United States with laboratory evidence of possible Zika virus infection during pregnancy have birth defects?

Findings  Based on preliminary data from the US Zika Pregnancy Registry, among 442 completed pregnancies, 6% overall had a fetus or infant with evidence of a Zika virus–related birth defect, primarily microcephaly with brain abnormalities, whereas among women with possible Zika virus infection during the first trimester, 11% had a fetus or infant with a birth defect.

Meaning  These findings support the importance of screening pregnant women for Zika virus exposure.

Abstract

Importance  Understanding the risk of birth defects associated with Zika virus infection during pregnancy may help guide communication, prevention, and planning efforts. In the absence of Zika virus, microcephaly occurs in approximately 7 per 10 000 live births.

Objective  To estimate the preliminary proportion of fetuses or infants with birth defects after maternal Zika virus infection by trimester of infection and maternal symptoms.

Design, Setting, and Participants  Completed pregnancies with maternal, fetal, or infant laboratory evidence of possible recent Zika virus infection and outcomes reported in the continental United States and Hawaii from January 15 to September 22, 2016, in the US Zika Pregnancy Registry, a collaboration between the CDC and state and local health departments.

Exposures  Laboratory evidence of possible recent Zika virus infection in a maternal, placental, fetal, or infant sample.

Main Outcomes and Measures  Birth defects potentially Zika associated: brain abnormalities with or without microcephaly, neural tube defects and other early brain malformations, eye abnormalities, and other central nervous system consequences.

Results  Among 442 completed pregnancies in women (median age, 28 years; range, 15-50 years) with laboratory evidence of possible recent Zika virus infection, birth defects potentially related to Zika virus were identified in 26 (6%; 95% CI, 4%-8%) fetuses or infants. There were 21 infants with birth defects among 395 live births and 5 fetuses with birth defects among 47 pregnancy losses. Birth defects were reported for 16 of 271 (6%; 95% CI, 4%-9%) pregnant asymptomatic women and 10 of 167 (6%; 95% CI, 3%-11%) symptomatic pregnant women. Of the 26 affected fetuses or infants, 4 had microcephaly and no reported neuroimaging, 14 had microcephaly and brain abnormalities, and 4 had brain abnormalities without microcephaly; reported brain abnormalities included intracranial calcifications, corpus callosum abnormalities, abnormal cortical formation, cerebral atrophy, ventriculomegaly, hydrocephaly, and cerebellar abnormalities. Infants with microcephaly (18/442) represent 4% of completed pregnancies. Birth defects were reported in 9 of 85 (11%; 95% CI, 6%-19%) completed pregnancies with maternal symptoms or exposure exclusively in the first trimester (or first trimester and periconceptional period), with no reports of birth defects among fetuses or infants with prenatal exposure to Zika virus infection only in the second or third trimesters.

Conclusions and Relevance  Among pregnant women in the United States with completed pregnancies and laboratory evidence of possible recent Zika infection, 6% of fetuses or infants had evidence of Zika-associated birth defects, primarily brain abnormalities and microcephaly, whereas among women with first-trimester Zika infection, 11% of fetuses or infants had evidence of Zika-associated birth defects. These findings support the importance of screening pregnant women for Zika virus exposure.

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