Babies that are more than two weeks overdue are twice as likely to develop attention deficit hyperactivity disorder (ADHD), recent research has found.

The longer a baby spends in the womb, the higher the chance of developing "problem behaviour", according to findings published in the Journal of Epidemiology.

"They are more than twice as likely as term born children to have clinical ADHD," the authors wrote.

Researchers studied 5145 post-term babies born between 2001 and 2005 in The Netherlands, looking at the link between time spent in the womb and behavioural and emotional problems as preschool children.

The findings are seen to be "perfectly plausible" by Professor Neena Modi, an expert in neonatal medicine at Imperial College London and the Royal College of Paediatrics.

"We know that birth after your due date is associated with a whole range of problems," she told The Guardian.


"If your baby stays in the womb for too long they are more likely to be a stillbirth, or weigh too little or become more likely to have a neurological disorder, because the longer a baby stays in the womb, the more likely the placenta is to stop functioning normal," she said.

Other factors like, maternal weight and height, ethnicity, family income, alcohol consumption, smoking, education level or even the mother's mental health at the time of pregnancy, didn't affect the outcome, Medical Daily reported.

The authors explained that larger babies tend to have a higher risk for perinatal problems. In addition, when babies are in the womb they are in "old" placenta which offers less nutrients and oxygen than what is given to a full-term foetus.

Alternatively, the more complicated birth process used in late births could cause emotional and behavioural problems, reported the Medical Daily.

More research is needed to show if the link between post-term pregnancies and the development of emotional and behavioural problems carries on after the child turns three, said lead researcher Hanan El Marroun.