THURSDAY, March 2, 2017 (HealthDay News) -- Pregnant women infected with the Zika virus are 20 times more likely to have a baby born with certain birth defects as mothers who gave birth before the Zika epidemic began, U.S. health officials reported Thursday.
Even worse, "when you look just at brain abnormalities and microcephaly, what we are seeing is more than 30 times higher than the prevalence before Zika was introduced to the Americas," said Margaret Honein. She is chief of the birth defects branch at the U.S. Centers for Disease Control and Prevention.
With microcephaly, babies are born with a smaller-than-normal head and an underdeveloped brain. Since the mosquito-borne virus first began to spread through South America in April 2015, thousands of babies have been born with Zika-linked microcephaly. The large majority have been born in Brazil, but the consequences of Zika infection during pregnancy are now being seen in the United States.
The increase in these types of birth defects is very large, Honein stressed.
"It really emphasizes the devastating effects that Zika virus can have on pregnant women and their babies, and the critical importance of preventing Zika virus infection during pregnancy," she said.
However, it is important to note that the absolute risk of these birth defects is still small when you look at all pregnant women in the United States.
Dr. Janet Cragan, a medical officer in the birth defects branch of the CDC, noted that in this report the investigators only looked at the physical abnormalities present at birth.
Although Zika can cause other developmental issues later, Cragan doesn't believe they have a handle on the extent of those problems yet. "We don't feel we have data on the full range of outcomes that may occur," she explained.
Honein added, "It is important that we follow up the infants to identify any development disabilities that may not be recognized initially, but may have profound effects later in life."
To get an idea of the extent that Zika increased the risk for birth defects, the researchers looked at the incidences of brain abnormalities, including microcephaly, neural tube defects and other early brain malformations, eye defects and other central nervous system problems among babies born in 2013 and 2014, before the Zika virus began circulating in South America.
The researchers found that three infants in every 1,000 births had such birth defects.
However, the proportion of babies with these types of birth defects who were born to women with Zika in 2016 was about 6 percent -- nearly 60 of every 1,000 infants, the findings showed.
To come up with the incidences of birth defects before Zika, the researchers looked at three programs that keep track of birth defects -- in Massachusetts, North Carolina and Georgia. The investigators believe that incidences of birth defects in these three locations are representative of the United States as a whole.
To assess the effects of Zika, the study authors compared that baseline number with the number of birth defects among pregnant women with Zika, as listed in the U.S. Zika Pregnancy Registry.
The researchers found 747 infants and fetuses with one or more of these defects from the programs in the three states they analyzed. Brain abnormalities, including microcephaly, were the most common conditions reported.
The report was published March 3 in the CDC's Morbidity and Mortality Weekly Report.
"Currently, there are over 1,500 pregnant women in the U.S. with possible evidence of Zika virus infection, and over 50 infants and fetuses have been born in the U.S. with one of these Zika-related birth defects," Honein said.
To prevent being infected with Zika and having a child born with a birth defect, the CDC continues to recommend that pregnant women not travel to areas where Zika is endemic.
If a pregnant woman has to travel to or lives in an area where Zika is circulating, she should talk with her doctor and take steps to prevent mosquito bites and sexual transmission of Zika, Honein said.
Dr. Jill Rabin, from the Women's Health Programs-PCAP Services at Northwell Health in New Hyde Park, N.Y., advises women who are planning to get pregnant not to travel to areas with Zika and not to have sex with men who may have been exposed to Zika.
"If you are in an area where Zika is, protect yourself from being bitten by wearing protective clothing and mosquito repellent," she said. "If you have been to a Zika-infested area, you may want to be screened for the virus even if you don't have symptoms," she added.
The World Health Organization has more on Zika.
This Q & A will tell you what you need to know about Zika.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.