Being born even a couple of weeks early can affect a child's math and reading skills, a new study suggests.

Children born at weeks 37 and 38 had lower reading and math scores than children born a week or two later, according to a study published in the journal Pediatrics. A normal pregnancy lasts about 40 weeks and children born at week 37 or later are considered full term.

It's long been known that children born early or preterm are at risk of developmental delays that can cause children to struggle academically. Little was known about developmental differences among children born within the full-term range of weeks 37 to 41.

The study, led by researchers at Columbia University Medical Center and New York-Presbyterian Hospital, is among the first to look at academic achievement among children considered full term.

Although differences in test scores by birth week were small, the study showed higher scores for both reading and math the later children were born. Children born at weeks 37 and 38 had the lowest scores compared with children born later.