"There has been quite a lot of research on very preterm birth and the increased risk for ADHD but less evidence when it comes to late preterm birth (weeks 34-36) and even less regarding babies born early term (weeks 37-38)," said Dr. Minna Sucksdorff, University of Turku in Finland.
Researchers compared about 10,321 children with ADHD against 38,355 children without ADHD but similar in terms of gender, birth date, and place of birth. They used medical records to identify their gestational age at birth and also looked at their weight during birth.
They found that the children with ADHD had more than 10 times greater odds of being born at 23 or 24 weeks of pregnancy than the children without ADHD. Also children with ADHD were at least twice as likely to be born between 27 and 33 weeks, compared to those without ADHD. The risk was also increased when weight for gestational age was 1 SD below and 2 SD above the mean.
This findings remained the same even after the researchers took into account other factors that affect gestational age and ADHD risk, such as the mother's age and whether she smoked or used drugs or alcohol.
"This highlights the importance of taking into account both prematurity and poor fetal growth when planning the timing of birth as well as later follow-up and support policies," said the authors.