Study: No Zika–Microcephaly Link Late in Pregnancy

Babies born to mothers infected with Zika during the third trimester have a low risk of developing microcephaly, researchers report.

Jun 17, 2016
Catherine Offord

FLICKR, TATIANA VDBZika has been linked to microcephaly and other birth defects in babies born to mothers infected with the virus. However recent research has hinted that this association is strongest during the first trimester, and trails off as the pregnancy continues. A preliminary study published earlier this week (June 15) in The New England Journal of Medicine lends support to that theory, reporting that mothers infected with the virus in the third trimester of pregnancy are unlikely to give birth to babies with noticeable defects.

“I think it’s somewhat reassuring that there were not major birth defects identified” following infection during the third trimester, study coauthor Margaret Honein of the US Centers for Disease Control and Prevention (CDC) told NPR’s Goats and Soda. “But I want to make sure we understand there is still a lot that we need to know.”

The data for the study came from national surveillance of Zika cases in Colombia since August 2015. Researchers found that, of the 1,850 women infected with the virus during the third trimester of pregnancy, more than 90 percent gave birth to infants without any “apparent abnormalities,” the CDC-led team wrote in its paper.  

The results are in line with previous observations of data collected in Brazil, University of Pittsburgh public health researcher Ernesto Marques, who was not involved in the research, told Science News. However, he added that it would be premature to conclude that there was no risk due to infection during the third trimester. “The fact that these babies do not have an anatomical problem does not mean that they do not have any problem,” he said. “We need to follow the development of these kids.”

The team also reported that Zika could pose a risk to fetuses even in mothers who showed no symptoms of infection, following the identification of four babies born with microcephaly to mothers who were asymptomatic. “We do think the majority of Zika virus infections are asymptomatic,” Honein told STAT News.

The report follows on a statement earlier this week (June 14) by the World Health Organization, advising pregnant women to avoid travel to “areas of ongoing Zika virus outbreaks,” and announcing that this year’s Olympic and Paralympic Games in Rio de Janeiro need not be postponed or canceled due to concerns over Zika.