CDC: 51 US Pregnancies Had Zika-Related Defects in 2016

Alicia Ault

April 04, 2017

Forty-four states reported pregnant women with evidence of Zika in 2016, and 51 of those pregnancies resulted in a fetus or a baby with Zika-related birth defects, according to a new report by the Centers for Disease Control and Prevention (CDC).

Those 51 cases — 45 live births and 6 pregnancy losses — accounted for 5% of a total of 972 completed pregnancies with evidence of Zika infection in the United States. Brain abnormalities and/or microcephaly were reported in 43 of 51 of the cases. For women with laboratory-confirmed infection, the rate of birth defects increased to 10% (24 of 250 completed Zika-confirmed pregnancies).

The analysis — which CDC officials said is the largest to date of Zika-associated pregnancy outcomes — is taken from the US Zika Pregnancy Registry, which covers the 50 states, the District of Columbia, and all US territories and includes data on pregnant women and infants up to a year old. It excludes Puerto Rico, which has a separate registry.

The 51 cases could be the tip of the iceberg. "Our current data might significantly underestimate the impact of Zika," said Peggy Honein, PhD, co-lead, Pregnancy and Birth Defects Task Force, CDC Zika Response, in a press briefing. 

First, symptomatic women are more likely to be tested, which can bias the registry. Current testing can identify only recent infections, which means some Zika will be missed — and the tests can't easily discriminate between various flavivirus infections.

Finally, something like 75% of clinicians are not following CDC guidance to conduct testing and neuroimaging of babies born to Zika-infected mothers, which means some defects could be missed, said Anne Schuchat, MD, the CDC's acting director, in the briefing.

She cautioned Americans against complacency, noting that currently, more than 1600 pregnant women have evidence of Zika infection — among the more than 5000 cases of the virus reported nationwide — and that warm weather, with a new mosquito season, is on its way to the United States. "We're still seeing about 30 to 40 new cases in pregnant women each week in the US," Dr Schuchat told reporters.

"Zika continues to be a threat to pregnant women in the US," she said. Dr Schuchat urged pregnant women to curb nonessential travel to Zika areas, and for those who must travel to those regions — and their partners — to prevent mosquito bites and to use condoms or abstain from sex.

Pregnancy Losses Not Explained

The CDC report, published in the Morbidity and Mortality Weekly Report on April 4, updates previously published birth defect estimates. Of the 1297 women with evidence of possible Zika infection reported to the registry, 972 had completed pregnancies, which included 895 liveborn infants and 77 pregnancy losses.

The report did not give any further detail on the losses. When asked by Medscape Medical News to comment on the reasons for the losses, Dr Honein said, "To protect confidentiality, we only report pregnancy losses as one group. Pregnancy losses include miscarriages that occur before 20 weeks gestation, stillbirths that occur at 20 weeks gestation or later, and terminations of pregnancy."

Of the 44 states that reported pregnant women with evidence of Zika last year, most of the women acquired their infection from travel, although some were exposed in the United States, said Dr Schuchat. The CDC will not be reporting pregnancies or defects on a state-by-state basis. "We have a certificate of confidentiality to do this work, and we really are protecting the privacy of women and families involved here," Dr Schuchat told reporters.

All 51 women whose pregnancies resulted in birth defects had been exposed during travel to 16 countries and territories: Barbados, Belize, Brazil, Cape Verde, Colombia, Dominican Republic, El Salvador, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Puerto Rico, Republic of Marshall Islands, and Venezuela.

Being symptomatic did not predict birth defects; abnormalities were reported in similar proportions of fetuses and infants whose mothers were or were not symptomatic. Women with confirmed Zika infections in the first trimester were at high risk for having a fetus or infant with birth defects.

Clinicians Not Following Guidance

Dr Schuchat said clinicians could do more to help identify Zika in women and infants and to treat and manage its related defects. It is rare. But because it has been found in pregnancies in 44 states and Washington, DC, doctors should be prepared, she said.

The data show that of the 895 infants born alive (of the 972 completed pregnancies), only 585 (65%) were tested for Zika virus. An even smaller number were given postnatal neuroimaging — 221 of the 895 infants born alive. CDC's "Interim Guidance for the Evaluation and Management of Infants With Possible Congenital Zika Virus," issued in August 2016, stated that postnatal neuroimaging and testing should be routine for all infants born to women with confirmed Zika during pregnancy.

That guidance had little impact on practice — before it was issued, only 20% of babies were given brain imaging after birth. Afterward, just 28% of babies born between September and December 2016 were given postnatal imaging.

Dr Schuchat said the reasons for a lack of imaging were "likely complex" and added that "there are opportunities here for improved monitoring." The CDC has no data on whether access to care or insurance restrictions might play a role in the limited follow-up. The low response may also mean that "clinicians are not yet aware of the value of brain scanning," said Dr Schuchat.

Babies may appear healthy at birth but have underlying brain defects or other Zika-related health problems that cannot be determined without comprehensive follow-up testing, including neuroimaging, said the CDC. "[C]omplete follow-up and routine developmental assessment of all infants born to women with laboratory evidence of possible recent Zika virus infection is essential to help identify future outcomes potentially associated with congenital Zika virus infection and ensure that the referrals to appropriate support and follow-up care are made," write CDC researchers in the new MMWR report.

Dr Schuchat said the agency hoped the new data "will increase awareness" and lead to greater testing, neuroimaging, and follow-up, including coordinating care plans with women who have Zika-affected infants.

"We do know this devastating outbreak is far from over, and the consequences of this outbreak are heartbreaking," said Dr Schuchat.

MMWR Morb Mortal Wkly Rep.  Published online April 4, 2017. Full text

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