According to the CDC, the study showed during the first trimester, women in the US territories with confirmed Zika infection had a baby or fetus with Zika-related birth defects 8 percent of the time.
That frequency dropped to 5 percent in the second trimester and 4 percent in the third trimester.
The nine-month average was just over 5.5 percent.
The analysis is based on information from more than 2,500 women who completed their pregnancies last April in American Samoa, Puerto Rico, the Virgin Islands, the Federated States of Micronesia and the Marshall Islands.
Last year, American Samoa reported more than 200 Zika cases, and at one point, declared a Zika epidemic.
Of the 2549 pregnancies reviewed, 122 women had babies or fetuses with birth defects, including microcephaly, the most high-profile abnormality linked to Zika.
Photo: AFP The risk of zika-related defects falls during each trimester according to the study