The Zika virus has sparked international alarm largely because of fears that the pathogen is causing microcephaly, a condition in which babies are born with unusually small heads and damaged brains.
But the preliminary results of a study released Friday suggest Zika can also cause other potentially grave complications for fetuses carried by women who get infected while they are pregnant.
"There seems to be a whole spectrum of conditions that are related to this — not only microcephaly," says Karin Nielsen-Saines, a professor of clinical pediatrics at the David Geffen School of Medicine at UCLA who led the study.
The analysis, based on the first 42 women in a larger ongoing study, found that Zika appears to increase the risk for miscarriages, poorly developed placentas, low or no amniotic fluid, severe growth problems, other kinds of brain damage, blindness and deafness, according to a preliminary report published in the New England Journal of Medicine.
The results "make a very strong case for Zika virus being the cause of all these pregnancy outcomes that are not very good," Nielsen-Saines says.
She cautions, however, that the study is still small and needs to be confirmed by following many more women for longer periods of time.
The link between Zika and microcephaly remains largely circumstantial. It's based on the observation that the number of cases of microcephaly appear to have increased in Brazil since the virus became epidemic in that country. Researchers have also found evidence of Zika in the brains of a handful of babies with microcephaly who died shortly after birth.
Concern about a possible link sparked a rush of studies to test the possibility, as well as explore whether the virus is causing other problems.
The new results mark the first from a prospective study, which involves tracking the health of women who are infected with Zika and comparing them to very similar people who are not infected.
"The take-home message is that this is another important addition to the growing evidence that seems to now be quite compelling of the relationship between infection of pregnant women and the development of congenital abnormalities," says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
For the study, Nielsen-Saines and colleagues from Brazil identified 88 women in the Rio de Janeiro area who had symptoms of Zika when they were pregnant. Seventy-two of the women had their Zika infection confirmed by polymerase-chain reaction (PCR) testing, which can identify genetic material from the virus.
Forty-two of those women, as well as 16 women who did not test positive for Zika, underwent ultrasounds to examine their fetuses. The ultrasounds of 12 of the infected women — 29 percent — found abnormalities. None of the Zika-negative women's ultrasounds found any problems.
Five of the fetuses being carried by the Zika-infected women were not growing normally; seven had central nervous system abnormalities; and seven had abnormalities in amniotic fluid volume or blood flow. In some cases, placentas didn't seem to be developing normally.
The problems observed on the ultrasounds are being explored and confirmed as the babies are being born. For example, two of the infants have lesions in their retinas, Nielsen-Saines says, which means they might be blind. And she said that some may be deaf. Two were born extremely small, which means they could experience complications of low birth weight. One baby was born with microcephaly.
And some of the fetuses are not making it to birth. There were two miscarriages early in the pregnancies, and two stillbirths just a few weeks before the babies were due, Nielsen-Saines says.
Other experts say the results are alarming, given the scope of the Zika outbreak.
"Millions are being affected as the epidemic has spread throughout the Americas," says Albert Ko, a professor of epidemiology at the Yale School of Public Health, who is studying Zika in Brazil. So, yes, I think this is very disturbing."
KELLY MCEVERS, HOST:
Researchers are sounding a new even more dire warning today about the possible threat the Zika virus poses to fetuses. A study suggests Zika is causing more complications among developing babies than had been thought before. NPR health correspondent Rob Stein reports.
ROB STEIN, BYLINE: Until now, the big worry about Zika is that it's causing a birth defect known as microcephaly. These babies have shrunken heads and badly-damaged brains, but doctors like Karin Nielsen-Saines at UCLA have been worried that Zika could be causing all kinds of other problems.
KARIN NIELSEN-SAINES: That microcephaly was just, like, the tip of the iceberg.
STEIN: So Nielsen-Saines started studying pregnant women who caught Zika in Rio de Janeiro. Today, she's reporting what she found out about the first 42 women. First of all, their ultrasounds spotted something wrong - seriously wrong - with one-third of the fetuses.
NIELSEN-SAINES: There seems to be, like, a whole spectrum of conditions that are related to this, not only microcephaly. Microcephaly is just one isolated finding. There's more.
STEIN: For example, many are just not growing normally. Some have other kinds of brain damage. The researchers aren't seeing anything like this when they look at pregnant women who don't have Zika. And the problems on the ultrasounds are becoming clearer as the babies are being born.
NIELSEN-SAINES: Two of the children have lesions in their retina, which means that they might be blind.
STEIN: Some maybe deaf. Two are really small, which means they'll have lots of complications - one is microcephaly and some aren't even making it.
NIELSEN-SAINES: We had two miscarriages early on, but then we had another two miscarriages - babies who died two weeks before being born.
STEIN: Taken together, Nielsen-Saines says the outlook is disturbing.
NIELSEN-SAINES: It makes a very strong case for Zika being the cause of all these pregnancy outcomes that are not very good.
STEIN: Now, Nielsen-Saines cautions that the study is small and needs to be confirmed by a lot more follow-up. But other experts say this is the strongest evidence yet of the danger Zika poses to pregnant women. Anthony Fauci is the top infectious disease expert at the National Institutes of Health.
ANTHONY FAUCI: The take-home message is that this is another important addition to the growing evidence that seems to now be quite compelling of the relationship between infection of a pregnant woman and the development of congenital abnormalities.
STEIN: And Albert Ko of Yale University says it's foreboding given the scope of the Zika outbreak.
ALBERT KO: Millions are being affected as the epidemic is spread throughout the Americas, and 30 percent of these women infected have these severe outcomes. So yes, I think this is very disturbing.
STEIN: These researchers and others plan to follow up with a lot more women for a lot longer to find out just how much of a threat Zika poses during pregnancy. Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.