A new study at Liverpool University has found that overweight pregnant women are more likely to be overdue and have more complicated births.
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.
For the study, the research team 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.
The study found more than a third of obese women had their labour induced, compared with just over a quarter of normal weight women.
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.
"Maternal obesity has become one of the most commonly occurring risk factors in obstetric practice including greater risk of prolonged pregnancy," the Telegraph quoted Dr Sarah Arrowsmith, from the University of Liverpool's Institute of Translational Medicine, and lead author on the paper as saying.
The study has been published in the British Journal of Obstetrics and Gynaecology.