This post has been updated.

The 20-year-old Brazilian woman never had any symptoms of Zika. And, yet, 32-weeks into her pregnancy, the expectant mother delivered a dead baby, which researchers believe may have been the result of the Zika virus.

Researchers already suspect (although have not yet proven) that Zika is associated with microcephaly, a condition which results in babies being born with unusually small brains. The condition causes a range of cognitive and physical disabilities, and in rare cases, can prove fatal. Now, a case study of a Brazilian women who suffered a stillbirth, published today (Feb. 25) in PLoS Neglected Tropical Diseases, has them concerned that the virus be associated with additional fatal birth defects.

The woman in the case study seemed to have a normal pregnancy at the start, researchers from the Yale School of Health wrote. Her 14-week ultrasound showed nothing out of the ordinary. At 18 weeks, however, doctors noticed that her baby was far below the average weight for a fetus at that age. After follow-up visits in her 26th and 30th week of pregnancy showed additional malformation, doctors informed her about the fetus’ abnormal development, which they believed could prove to be fatal for the child.

Doctors induced labor at 32 weeks when they saw that her baby suffered from hydrop fetalis, a deadly condition that causes the formation of pockets of fluid in the brain and chest of the child. Later tests confirmed that the Zika virus was present in the baby’s cerebrospinal fluid (found in the brain and spine) and amniotic fluid (which holds the baby in the womb).

“These finding raise concerns that the virus may cause severe damage to fetuses leading to stillbirths and may be associated with effects other than those seen in the central nervous system,” Albert Ko, an epidemiologist the Yale School of Public health and lead author of the paper, said in a press release. Stillbirth occurs when a fetus dies after 20 weeks of pregnancy. The mother may still have contractions and go through childbirth.

It’s not yet clear whether or not Zika caused the defects in this individual case. Hydrop fetalis can be caused by many factors, including other viruses, such as CMV. But the occurrence of the virus in the central nervous system is nevertheless alarming, because it suggests that the virus may have played a role in the baby’s cranial deformities. The study’s authors hope that their case study will prompt researchers in Zika-affected regions to check for the presence of the virus in cases of stillbirths or hydrancephaly (where there is only fluid instead of the child’s brain).

Zika virus has been spreading rapidly throughout the Americas and infected millions. Most infected people are asymptomatic. When adults do become ill, they develop a fever, rash, joint pain, and conjunctivitis. A small proportion might also suffer from Guillain-Barré syndrome, which causes temporary paralysis.

The World Health Organization has urged countries to proceed as if Zika causes these birth defects. Governments have warned residents of, and travellers to Zika-affected countries to practice safe sex and postpone having children, if possible.

This post was updated to include that microcephaly can be fatal in rare cases.