A study led by investigators at the University of California, Los Angeles, has found that Zika-linked abnormalities that occur in human fetuses are more extensive—and more severe—than previously thought, with 46% of 125 pregnancies among Zika-infected women resulting in birth defects in newborns or ending in fetal death.
The findings, published in the New England Journal of Medicine, suggest that damage during fetal development from the mosquito-borne virus can occur throughout pregnancy and that other birth defects are more common than microcephaly. Further, these defects may not be detectable until weeks or months after the baby is born, according to senior author Dr. Karin Nielsen.
“This means that microcephaly is not the most common congenital defect from the Zika virus,” Nielsen said. The absence of that condition does not mean the baby will be free of birth defects, she added, because “there are problems that are not apparent at birth,” and such difficulties may not be evident until the age of six months.
“These are sobering results,” Nielsen said.
The study is a follow-up to a smaller Brazilian investigation published in March that used molecular testing to find an association between Zika infection in pregnant women and a series of serious outcomes that included fetal deaths (miscarriages and stillbirths), abnormal fetal growth, and damage to the central nervous system. The UCLA study is the largest investigation to date of Zika-affected pregnancies in which the women were followed from the time they were infected to the end of their pregnancies. All of the women were enrolled before any abnormalities in their pregnancies had been identified.
The new study was based on a sample size of 345 women in Rio de Janeiro, Brazil, who were enrolled from September 2015 through May 2016. Of those women, 182 (53%) tested positive for Zika in the blood, urine, or both. In addition, 42% of the women who did not have Zika were found to be infected with chikungunya, another mosquito-borne virus; 3% of Zika-positive women also had chikungunya.
The researchers evaluated 125 women infected with Zika and 61 not infected with the virus who had given birth by July 2016. The previous Brazilian study was based mainly on prenatal ultrasound findings; in contrast, the new research evaluated infants from Zika-affected pregnancies through physical examinations and brain imaging. The new findings included:
The risks of abnormalities occurred at all stages of pregnancy. Fifty-five percent of pregnancies were affected during the first trimester; 51% during the second trimester; and 29% during the third trimester.
The researchers noted that they examined the babies during their early infancy, when “more-subtle neurologic manifestations of disease are not identified.” Thus, their follow-up examinations could turn up evidence of more neurologic diseases that couldn’t be detected earlier in the babies’ lives.
“Our data show that the risk of severe adverse pregnancy and infant outcomes after maternal Zika infection was substantial,” the authors wrote.