Overweight pregnant women are more likely to be overdue and have more complicated births, a study has found.
Women who were overweight or obese before they conceived were more likely to have a longer pregnancy, need to have labour induced artificially and to go on to require caesarean section births.
The research was conducted by a team at Liverpool University who examined the records of almost 30,000 women who gave birth over four years.
Three in ten obese women were overdue, defined as still pregnant ten days after their due date, compared with around two in ten of healthy weight women.
More than a third of obese women had their labour induced, compared with just over a quarter of normal weight women, the study published in the British Journal of Obstetrics and Gynaecology found.
In addition almost three in ten obese women had an induction of labour which later resulted in a caesarean delivery compared to less than two in ten normal weight women.
However, more than seven in ten obese women still gave birth naturally and the rates of complications in labour and for the baby were the same as in normal weight women.
Other studies have found that maternal obesity is now one of the biggest risks in childbirth. In 2007 it was found that half of all women who died during pregnancy or soon after giving birth were overweight.
Maternity units have had to order special operating tables, wheelchairs and other equipment to deal with the increasing number of obese mothers and doors have had to be widened to accommodate them.
Management of obese prolonged pregnancies is often difficult as induction of labour is associated with a high risk of caesarean section and the possible complications that follow including infection, bleeding and clots.
Dr Sarah Arrowsmith, from the University of Liverpool’s Institute of Translational Medicine, and lead author on the paper said: “Maternal obesity has become one of the most commonly occurring risk factors in obstetric practice including greater risk of prolonged pregnancy.
"The importance of this research is that it investigates delivery outcomes for women who are obese with prolonged gestation and receiving labour induction. The fact that the majority of obese women did have a vaginal delivery, with labour complications being largely comparable to normal weight women, suggests that induction of labour in obese women with prolonged pregnancy is a safe method for managing these difficult pregnancies.
“Our findings were somewhat unexpected, given the well-reported complications surrounding obesity in pregnancy, but were clinically reassuring.
"Our current research is focused towards underlying causes of prolonged pregnancy, which can affect up to 10pc of women, as currently we know little about it."
Professor Philip Steer, BJOG editor-in-chief said: "Maternal obesity is on the rise and is associated with pregnancy complications. The risk of caesarean section is heightened when the woman is induced, however, it is promising to see that a large number of obese pregnant women delivered vaginally.”