March 14, 2018 — Birth defect rate pegged at 7 percent for babies born to Zika-infected women

By Gene Emery, Reuters Health

A pregnant woman who becomes ill from the Zika virus faces a 7 percent chance that her child will be born with birth defects, and that risk jumps to nearly 13 percent if she becomes ill during the first trimester, a new study conducted in French territories in the Americas has concluded. The finding “emphasizes the serious global health threat to pregnant women and their infants posed by congenital (Zika virus) infection,” said Dr. Margaret Honein of the Centers for Disease Control and Prevention in Atlanta in an editorial in the New England Journal of Medicine, where the study appears. The estimates do not include less-obvious developmental problems that may surface later in life. In addition, because the study only included women who fell ill, it does not include the risk for women who may have been infected but did not experience symptoms, which happens in about 80 percent of cases. “Other studies showed earlier that the risk of birth defects did not depend on the presence or the severity of (Zika)-related symptoms,” chief author Dr. Bruno Hoen of the University Medical Center of Guadeloupe told Reuters Health by email. Carl Fichtenbaum, a professor in the Division of Infectious Diseases at the University of Cincinnati College of Medicine in Ohio who was not involved in the research, said the birth defect rate might differ in other populations depending on whether it’s a first or second Zika infection. "In populations where it’s just been introduced it might be more severe for the fetus, but time will tell," he said.

The 527 surviving babies in the new study will be followed for at least two years. Only longer-term follow-up will help identify the full spectrum of Zika-related complications, the Hoen team said.

The virus was linked to birth defects, particularly microcephaly, during the 2016–2017 outbreak. Zika vaccines are still being tested. Previous estimates of congenital neurologic defects in infected newborns ranged from 6% to 42%.

The Hoen team included women who were pregnant from March through November 2016 and had confirmed Zika infection. Their study of 555 fetuses and infants found evidence of microcephaly in 5.8% and severe microcephaly in 1.6%. The earlier the infection in pregnancy, the greater the risk: neurologic or eye problems were seen in 12.7% of babies whose mothers were infected during the first trimester. The rates were 3.6 percent when mothers were infected during the second trimester and 5.3 percent during the third. "This is some of the most compelling data to date that the risk of brain abnormalities, microcephaly, and eye anomalies extends to infections in every trimester of pregnancy," Honein wrote in her editorial. The French territories were French Guiana, Guadeloupe, and Martinique. A Zika registry in the United States has found birth defects in 10 percent of women known to have been infected with the virus; when the infection occurred during the first trimester, the rate was 15 percent. But those studies "do not provide information on the estimated 80 percent of pregnant women with Zika infections who have no reported symptoms," Honein wrote. "Population-level increases in Zika-associated birth defects are unlikely to be recognized without ongoing, timely, and comprehensive surveillance of birth defects that captures all affected fetuses and infants regardless of whether maternal Zika exposure or infection was identified." Zika "should definitely be added to the list of infectious agents that can cause severe birth defects, as are rubella virus, cytomegalovirus, and others," Honein said in her email. The study also emphasizes the urgent need to protect women who may become pregnant while traveling or living in areas with Zika-infected mosquitoes, to test women at risk for Zika when they become pregnant, and to develop an effective vaccine, she said. The New England Journal of Medicine, online March 14, 2018.