Zika Holds 1 in 100 Risk of Microcephaly

The Zika virus has been linked to microcephaly—but we haven't had any real proof to support their association. Now, research supports their association.

Zika Holds 1 in 100 Risk of Microcephaly Brazil Photo Press/CON/Getty Images

Zika and its tie with microcephaly have been all over the news for the past few months—with the CDC issuing out warnings and updates continuously emerging. But stories like that of a Mexican woman who had contracted Zika and then gave birth to a healthy baby had the world wondering if the relationship between Zika and the condition was purely coincidental. Now, recent research in The Lancet suggests that, while Zika can certainly cause microcephaly, it might not always happen this way. The study estimates that one out of every 100 women who contract Zika during the first trimester of pregnancy will give birth to babies with the condition.

Understanding the risk

According to the authors, understanding this risk is essential to informing the broader public health response. If this research is any indication, the risk of microcephaly resulting from Zika is relatively low, certainly lower than we had previously thought. With that being said, this is still a major public health issue, especially since the risk is particularly high during outbreaks—which is exactly what we're seeing now in South America.

"Our analysis strongly supports the hypothesis that Zika virus infection during the first trimester of pregnancy is associated with an increased risk of microcephaly," Simon Cauchemez, Ph.D., co-author of the study, said. "We estimated that the risk of microcephaly was 1 in 100 women infected with Zika virus during the first trimester of pregnancy. The findings are from the 2013-14 outbreak in French Polynesia and it remains to be seen whether our findings apply to other countries in the same way."

Microcephaly is neurological abnormality that causes babies to be born with unnaturally small heads. It also involves reduction of brain volume, which causes intellectual disabilities, speech impairment and behavioral issues. About two in every 10,000 babies are born with microcephaly in Brazil and Europe.

What it means

During the 2013-2014 outbreak in French Polynesia, eight cases of microcephaly were diagnosed—five of these cases were terminated in pregnancy. Researchers used mathematical and statistical models to estimate the number of cases that may have been undiagnosed. They also looked at total number of births during that time period, the timing of cases of microcephaly and the trimester in which the mother was infected to come to their finding.

"Data from French Polynesia are particularly important since the outbreak is already over," Arnaud Fontanet, co-author of the study, said. "This provides us with a small, yet much more complete dataset than data gathered from an ongoing outbreak. Much more research is needed to understand how Zika might cause microcephaly."

While it appears the risk is greatest in the first trimester of pregnancy, it's suggested that you stick to the CDC's original recommendation—that pregnant women don't travel to areas of outbreak, regardless of what how far along they are. It's clear that we really can't fully understand the risks that come along with Zika until we see more research.

"The finding that the highest risk of microcephaly was associated with infection in the first trimester of pregnancy is biologically plausible, given the timing of brain development and the type and severity of the neurological abnormalities," Laura Rodrigues, London School of Hygiene & Tropical Medicine, UK, said in the study's release. "Further data will soon be available from Pernambuco, Colombia, Rio de Janeiro, and maybe other sites... The fast production of knowledge during this epidemic is an opportunity to observe science in the making: from formulation of new hypotheses and production of new results that will provide confirmations and contradictions to the refinement of methods and the gradual building of consensus."