A doctor performs physical therapy on an infant born with microcephaly in Brazil. (Photo by Mario Tama/Getty Images)

Physicians commonly detect microcephaly, a condition affiliated with the Zika virus, when babies are in the womb or first born. But according to a comprehensive new CDC study, some babies aren’t diagnosed until several months after birth.

Babies with microcephaly have heads that are smaller than children of their similar age and sex.

The study expands upon previous research by documenting how long it took before several infants who didn’t have microcephaly at birth started showing symptoms of the condition, as well as other brain abnormalities.

Researchers observed 13 infants who were born in Brazil between October 2015 and January 2016, and then evaluated them again between October 2015 and October 2016.

Eleven of them experienced slower head growth—the soonest at five months old. And they were eventually diagnosed with postnatal microcephaly. The other two infants were found to have other developmental concerns at 5 and 7 months old.

According to the report, some of the 13 infants were found to have cases of dysphagia, epilepsy, irritability, chorioretinal abnormalities, hypertonia, and spastic hemiparesis, among other issues.

In order to find trends and further research, scientists also collected information from the children’s mothers about demographic and medical information, including whether they recalled having a rash during pregnancy.

More information is needed to “fully describe the clinical spectrum of findings associated” with Zika infections, researchers said. They recommended continued medical care and follow-ups for infants who are exposed to Zika prenatally, even if they don’t show signs at birth.