Some pregnant women with Zika virus tend not to fare well, and neither do their fetuses, a new study finds.

Zika is a mosquito-borne virus that can also be transmitted through unprotected sexual intercourse. Because of concerns that the disease may increase the risk of microcephaly (small brain size) and other developmental disorders in the fetuses of pregnant women infected with the virus, scientists decided to monitor the pregnancies of both healthy and infected women.   

The researchers studied 88 pregnant women in Rio de Janeiro from September 2015 through February 2016, according to the study, published Friday (March 4) in the The New England Journal of Medicine. Of these women, 72 tested positive for Zika virus in their blood, urine, or both. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

Among the Zika-positive pregnant women, the most common symptoms were rash, joint pain, red eye and headache, the researchers found. The doctors also performed a fetal ultrasound on 42 of the women with Zika and on all of the women without Zika. Among the Zika-positive group, 12 of them (29 percent) had fetuses with abnormalities, compared to none of the 16 Zika-negative women.

Among the 12 fetuses with abnormalities, two of them died — one at 36 weeks and the other at 38 weeks. Five of the fetuses were smaller than normal (and some had microcephaly), seven had central nervous system lesions, and seven had an abnormal amount of amniotic fluid or cerebral or umbilical artery flow, the researchers said. One fetus had additional problems, including microcephaly and other brain development challenges, growth restriction and a potential clubfoot, they added.

To date, eight of the 42 women who participated in the ultrasound have given birth, and the ultrasonographic findings have been confirmed, the researchers said.

"Despite mild clinical symptoms, Zika virus infection during pregnancy appears to be associated with grave outcomes, including fetal death, placental insufficiency, fetal growth restriction and central nervous system injury," the scientists said in the study.

The findings are "quite disturbing," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters today (March 10) in a news briefing. 

Given that fetal abnormalities were found in 29 percent of the Zika-positive women,  it's possible there may be "many more [abnormalities] that you don't realize until after the birth of the baby," Fauci said. 

Moreover, the study shows that the fetuses had developmental problems even when their mothers caught the disease late in their pregnancies. 

"In all three trimesters of pregnancy, there were definite fetal effects," Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, told reporters in today's briefing. "What we're saying basically is that the more we learn about Zika in pregnancy, the more concerned we are."

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