New CDC Stats: Zika Birth Defects Appear in 10% of Babies Born to Mothers Infected While Pregnant

After a brief reprieve, Zika fear is back with a vengeance as the US mosquito population booms. And we're just now seeing the true impact of this devastating virus, as babies of mothers infected with the virus are being born.

About 10% of pregnant women confirmed as having been exposed to the virus during their pregnancy end up having babies with birth defects, according to a new case study from the Centers for Disease Control and Prevention (CDC).

A Zika virus infection can be anywhere from mild to devastating. Most infected people don't have any symptoms, but it can cause Guillain–Barré syndrome—a disorder that affects the immune system and damages nerves.

Additionally, if a pregnant woman gets the Zika virus, her baby may be born with a severely small head, called microcephaly, and other brain and medical problems. The frequency of this complication has been found to be anywhere between 1% and 13% in previous studies. These new estimates from the CDC's analysis of US mothers with confirmed cases of Zika seem to indicate that the occurrence is on the higher end of that spectrum, especially if the woman is exposed to the virus early in her pregnancy.

The statistics were drawn from the US Zika Pregnancy Registry, which keeps track of pregnant women who were suspected to have been infected with Zika from January to December 2016.

They tracked 972 completed pregnancies with possible Zika infections (based on symptoms and travel history), of which 51 of women reported birth defects, about 5% of the pool. But when looking specifically at the 250 pregnant women confirmed to have had Zika, 24 had a fetus or baby with Zika-related birth defects, which jumps the rate up to 10%.

That number jumps even higher, to 15%, when looking at women who are known to have contracted the virus in the first trimester of pregnancy.

This number may still be higher, as some defects may develop or become more obvious later in life.

Between January 1, 2015 and March 29, 2017, 5,182 US cases of Zika virus infection were reported to the CDC (not counting US territories). Florida has had the most, with 1,114 cases, while New York is in second place with 1,016 cases. Most of these cases were from travelers returning to the US after visiting a country of concern.

The only way to prevent infection in pregnant women is constant vigilance, as Peggy Honein, of Zika Response's Pregnancy and Birth Defects Task Force, put it in the press release:

CDC recommends that pregnant women avoid travel to areas with risk of Zika and unprotected sex with a partner who has traveled to an area with Zika to prevent Zika-related birth defects in their babies.

"Zika virus can be scary and potentially devastating to families. Zika continues to be a threat to pregnant women across the US," the CDC's Acting Director Anne Schuchat said in the press release. "With warm weather and a new mosquito season approaching, prevention is crucial to protect the health of mothers and babies. Healthcare providers can play a key role in prevention efforts."