Global fears about Zika virus may have waned since the disease first made headlines in 2015 – but scientists at the National Primate Research Centers continue to make important discoveries to understand and prevent its adverse effects during pregnancy.

Scientists at six NPRCs across the U.S. have recently collaborated on a study that concluded Zika may be responsible for more childbirth complications than originally thought – even when women show few symptoms during pregnancy.

The study, published in the journal Nature Medicine, showed that 26% of nonhuman primates inoculated with Zika in the early stages of pregnancy experienced miscarriage or stillbirth, despite displaying few clinical signs of infection. For scientists, this indicates that Zika-associated pregnancy loss in humans may be more common than previously believed, since the illness itself often goes undetected.

“The primary conclusion from this multi-center study with important implications for pregnant women infected with Zika virus is that stillbirth and miscarriage occur more frequently in infected nonhuman primates than animals not exposed to the virus,” explained lead author Dawn Dudley, PhD, with the Wisconsin National Primate Research Center.

This discovery matches human reports of adverse outcomes in babies exposed to Zika during the first trimester, helping to solidify the connection between Zika infection and its negative effects on pregnancy, even when symptoms are mild or absent. It also underlines the importance of frequent Zika testing for pregnant women – especially in regions where the disease has been identified.

In the U.S., infections have been reported in Florida and Texas. Now, the Texas Department of State Health Services is asking OB/GYNs in the counties bordering Mexico to test pregnant patients for Zika three times during pregnancy. In addition, all pregnant women across the country are cautioned to protect themselves against mosquito bites.