The list of "grave outcomes" found in the study of pregnant women in Rio de Janeiro, published in the New England Journal of Medicine on Friday, included fetal death, calcification of the brain, placental insufficiency with low to no amniotic fluid, fetal growth restriction and central nervous system damage, including potential blindness.

"These were women infected in the first and second trimester of pregnancy," Dr. Karin Nielsen, lead author of the study, said in a telephone interview.

"We also saw problems in the last trimester, which was surprising to us," added Nielsen, noting two cases of fetal death very late in pregnancies in which there was no sign of brain malformation in earlier ultrasound tests.

"We have found a strong link between Zika and adverse pregnancy outcomes, which haven't been documented before," said Nielsen, professor of clinical paediatrics at the David Geffen School of Medicine at UCLA. "Even if the foetus isn't affected, the virus appears to damage the placenta, which can lead to fetal death."

Zika infection has been linked to numerous cases in Brazil of the birth defect microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems.

Much remains unknown about Zika, including whether the virus actually causes microcephaly. Brazil said it has confirmed more than 640 cases of microcephaly and considers most to be related to Zika infections in the mothers. Brazil is investigating more than 4,200 additional suspected cases of microcephaly. Nielsen said microcephaly may be one of many abnormalities in what she referred to as Zika Virus Congenital Syndrome.

A separate case study reported last week in the journal PLOS Neglected Tropical Diseases described a stillborn baby from a Brazilian mother infected with Zika in which the skull was filled with fluid but had no brain.

The new study was conducted by researchers at UCLA and at the Fiocruz Institute in Brazil. It followed 88 women who went to a Rio de Janeiro clinic between September 2015 and last month, 72 of whom tested positive for Zika. No fetal abnormalities were detected in any of the 16 women who tested negative for Zika.

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