Post-term Babies Are More than Twice as Likely to Develop ADHD in Later Years

Research has found that post-term babies (babies in the womb longer than 42 weeks) are twice as likely to develop ADHD compared to babies that are normal term. This risk of ADHD was shown to have no affect from the mother's factors, such as height and weight. They also found that pre-term babies had the same risk of developing ADHD. These findings, however, did not have causality. A potential reason for this was that post-term babies are exposed to old placenta longer that has fewer nutrients and oxygen. It may also be a result of more complications with post-term births.

http://medicaldaily.com/news/20120503/9754/adhd-add-post-term-pre-term-birth-pregnancy.htm