A new study reveals that babies born earlier tend to do more poorly in school when compared to their later-born counterparts.

The new research shows that infants could benefit from that extra time spent in the womb, and that more time spent in utero can lead to increased brain development. The difference was true even of babies born on week 37 and 38, as compared to babies born a week or two later.

The study was led by Dr. Kimberly Noble, an assistant pediatrics professor at Columbia University Medical Center. They analyzed data from 128,000 8-year old New York City public school children and included a large number of economically disadvantaged children. The study authors insist that the results would be about the same, no matter what income group they were studying.

All the children born were considered full-term and normal gestation period was around 37 to 41 weeks.

When counting children born at 37 weeks, 2.3 percent of children had severely poor reading skills and 1.1 percent had moderately poor math skills, as compared to 1.8 percent and 0.9 percent, respectively, of children born at 41 weeks. Their chances of having poorer skills in reading and math, as compared to their peers born at 41 weeks, were 33 percent greater and 19 percent greater, respectively.

This study may have important implications for women planning to have elective Caesarean-section surgeries. Though some families love the idea of choosing a birth date for their new son or daughter, sometimes doctors’ week counts are a bit off – meaning that a Caesarean section scheduled for week 38 may actually be taking place during week 37. Caesarean sections should also be used more for medical reasons rather than the whim, or schedule, of the parents.

However, despite the fact that study authors insist on the consistency of results across income groups, it is not immediately clear whether researchers controlled for factors like socioeconomic level or number of children in the family – both of which may impact academic success.

The study was published in Pediatrics.