A new study involving pregnant women in Brazil shows further evidence of a link between the Zika virus and birth defects.

A preliminary report published in the New England Journal of Medicine on Friday, says that Zika infection during pregnancy “appears to be associated with grave outcomes,” which include microcephaly, the condition that causes abnormally small heads, fetal deaths and central nervous system malformations.

Between September, 2015 and February of this year, the study enrolled 88 pregnant women in Rio de Janeiro who had developed a rash within the previous five days.

Of those 88 women, 72 (or 82 per cent) tested positive for the Zika virus in their blood, urine or both. Two of them had miscarriages during their first trimester.

The main symptoms observed among the Zika-positive women were a rash, itchy skin, joint pain, headache and bloodshot eyes. Twenty-eight per cent of the infected women also developed a fever.

Ultrasound exams were performed on 42 Zika-positive women and all 16 Zika-negative women. Fetal abnormalities were detected in 12 of the 42 infected women, or 29 per cent. No fetal abnormalities were found in the women who tested negative for the virus.

Among the women who tested positive for Zika, there were two fetal deaths at 36 and 38 weeks of pregnancy. Five other fetuses had “growth restriction” with or without microcephaly.

Seven fetuses had ventricular calcifications or lesions within the central nervous system. Another seven fetuses had abnormal amniotic fluid content or abnormal cerebral, umbilical and placental artery flow, the study found.

To date, there have been six live births and two stillbirths among the 42 Zika-positive women. The abnormalities observed on ultrasounds have been confirmed in those babies, researchers say.

The study notes that all the Zika-positive women who had abnormal ultrasounds were otherwise healthy, “with no other risk factors for adverse pregnancy outcomes.”

“We believe that our findings provide further support for a link between maternal (Zika) infection and fetal and placental abnormalities that is not unlike that of other viruses that are known to cause congenital infections characterized by intrauterine growth restriction and placental insufficiency,” the researchers wrote in their conclusion.

Scientists have not yet been able to definitively prove that Zika causes microcephaly. But there is mounting evidence of a link between the two.

Another study released Friday found that Zika can infect embryonic cells that help form the brain. The study provides experimental evidence that once the virus reaches the developing brain, it can infect and harm cells that are key for further brain development.

The mosquito-borne Zika virus has been documented in 55 countries and territories since 2007, and has been rapidly spreading in Latin America and the Caribbean over the past year. 

The World Health Organization says that, so far, an increase in microcephaly cases and other neonatal malformations has only been reported in Brazil and French Polynesia. Two microcephaly cases linked to a stay in Brazil were reported in the United States and Slovenia.

Between Oct. 22, 2015 and Feb. 27, a total of 5,909 cases of microcephaly and/or central nervous system malformation were reported by Brazil, the WHO says in its latest Zika update. Those cases include 139 fetal deaths.

“This contrasts with the period from 2001 to 2014, when an average of 163 microcephaly cases was recorded nationwide per year,” the WHO says.