'If a child is still sleeping in the same room with you, you need to think about where your child is going to sleep in the long term.'

London - Babies who spend too long in the womb are twice as likely to suffer behavioural problems in early childhood, researchers have warned.

The added risk is similar to that of being born prematurely, which is known to cause health and emotional problems.

The first study of its kind found that babies born after a pregnancy of 42 weeks were twice as likely to have long-term problems compared with those born after about 40 weeks - the normal length of a pregnancy.

The findings will increase calls for women to be offered induction methods or a caesarean if their pregnancy becomes prolonged. The researchers, from the Netherlands, say the results may be due to the placenta failing to provide sufficient nutrients and oxygen after 40 weeks.

Their study followed the progress of 5,145 babies in Rotterdam for three years to investigate the relationship between the length of time spent in the womb and long-term behavioural and emotional problems. They found that 382 babies (seven percent) were born post-term, or beyond 42 weeks. The longest time spent in the womb was 43.7 weeks.

Of the others, 226 (4 percent) were born pre-term, which is classified as before 37 weeks.

The children’s parents completed questionnaires on their behaviour after 18 and 36 months. The researchers found that both post-term and pre-term babies were at a higher risk of behavioural and emotional problems at these stages.

Post-term children were almost twice as likely as children born around 40 weeks to have such problems, including attention deficit hyperactivity disorder (ADHD). Symptoms include impulsiveness, restlessness and hyperactivity.

The study’s lead author Dr Hanan El Marroun said: “Children born too late are more than twice as likely as term-born children to have clinical ADHD.” She added that the risk for those born too early is “similar”.

“We were aware of potential complications caused by babies born prematurely, but these findings suggest there is also a greater risk of long-term problems among babies born too late,” she warned. Dr El Marroun said the overall rate of emotional and behavioural problems was two percent, rising to four percent among early and late babies.

She explained that those who spend longer than 40 weeks in the womb tend to be bigger. The “old” placenta cannot provide the level of nutrients and oxygen they require, she said, which may lead to abnormal physical, emotional and behavioural development.

She suggested that, “based on our findings and previous research, it would be advisable to induce labour or offer a c-section” at between 40 and 41 weeks, “because it might reduce emotional problems and has the advantage of pre-empting some of the other complications involved when women give birth to bigger babies”. - Daily Mail

Her team’s research is published in the International Journal of Epidemiology.