Women who are overweight are prone to longer pregnancies and complications during birth, a new study has suggested.
Researchers analysed the data of more than 100,000 women who gave birth between 1998 and 2002 to see what effect a high body mass index (BMI) had on pregnancy.
About 6.8% of the pregnancies they looked at were delivered post-date – after more than 42 weeks.
A higher BMI during the first trimester was associated with a longer gestation, the team found.
A change in BMI between the first and third trimesters was also linked with longer pregnancies and a higher risk of complications, the research found.
A team including Dr Fiona Denison from Edinburgh University's Queen's Medical Research Institute analysed data from the Swedish Medical Birth Register.
It concluded: "Maternal obesity poses a significant risk to maternal and foetal health during pregnancy, and our study confirms that obesity is associated with significant complications including stillbirth, gestational diabetes, pregnancy-induced hypertension and caesarean section."
Around 60,000 women deliver after 40 weeks each year in the UK and, compared with babies delivered at term, these children are at greater risk of developing conditions such as epilepsy and Asperger's syndrome in later life, the study said.