CDC Releases Estimates on Proportion of Infants Who Will Suffer Birth Defects After Maternal Zika Virus Infection

Roughly 1 in 12 infants born to mothers with confirmed Zika virus infection are born with a related birth defect, a Centers for Disease Control and Prevalence (CDC) analysis has concluded.

The sobering findings were published in the Morbidity and Mortality Weekly Report (MMWR) for June 16, 2017.

Of course, research conducted since the first outbreak of the mosquito-borne virus was reported in Brazil in 2014 has linked the disease with birth defects such as microcephaly and various neurological deficits during early infancy. The problems are particularly acute among infants born to mothers infected with Zika during the first trimester of pregnancy.

For the CDC study, researchers at the agency abstracted data from its Zika pregnancy and infant registries collected between January 1, 2016 and April 25, 2017. They focused on completed pregnancies involving mothers with laboratory evidence of recent possible Zika virus infection and a subset with positive nucleic acid tests (NAT) confirming Zika virus infection (NAT-confirmed).

The authors analyzed the registries and identified fetuses and/or infants with birth defects meeting the CDC Zika surveillance criteria and classified them into 2 distinct categories: with one encompassing those with “brain abnormalities and/or microcephaly and the other including those with neural tube defects, eye abnormalities, or consequences of central nervous system dysfunction among fetuses or infants without evidence of other brain abnormalities or microcephaly.”

In all, 3930 pregnancies in US territories with laboratory evidence of recent possible Zika infection were reported to the registries during the study period. These pregnancies resulted in 2464 “live-born” infants and 85 pregnancy losses. A total of 61% of the women with completed pregnancies had signs or symptoms compatible with Zika virus infection during pregnancy. Maternal symptoms or positive laboratory test results were recorded in the first, second, and third trimesters for 21%, 43%, and 34% of the women included in the analysis, respectively.

Overall, of the completed pregnancies, 122 fetuses or infants (5%) had possible Zika-associated birth defects, with 108 having brain abnormalities and/or microcephaly. Among the 1508 pregnancies in women with NAT-confirmed Zika, a total of 5% resulted in fetuses or infants with possible related birth defects. Among pregnant women with NAT-confirmed infections, possible Zika-associated birth defects were reported in 8%, 5%, and 4% of infants or fetuses with symptoms or lab results reported during the first, second, and third trimesters, respectively.

“This report adds information about the number of possible Zika-associated birth defects with laboratory evidence of recent possible or NAT-confirmed Zika virus infection during pregnancy among women,” stated the authors in their concluding remarks. They continued, “It also provides new estimates for the proportion of infants with a birth defect after identification of maternal Zika virus infection in the first, second, and third trimesters of pregnancy, and provides evidence that birth defects might occur following documentation of symptom onset or positive laboratory testing during any trimester. Moreover, based on data reported to the pregnancy and infant registries, this report highlights potential gaps in testing and screening of infants with possible congenital Zika virus infection in US territories at birth. Identification and follow-up of infants born to mothers with laboratory evidence of recent possible Zika virus infection during pregnancy can facilitate timely and appropriate clinical intervention services and assessment of future needs.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.