The team from the University of Liverpool conducted a research on 4,000 pregnant women and found that one in five obese women had to undergo emergency Caesarean section birth as the muscles in their uterus failed.

Obese women were 3.5 times more likely to require a Caesarean for slow labor than non over-weight women.

Overweight pregnant women who gave birth vaginally also encountered more problems during and after delivery and were twice as likely to experience excessive bleeding following delivery. Excessive bleeding happens when the uterus is not able to contract well enough to clamp off the blood vessels that are sheared following delivery of the placenta.
These findings show that overweight women find labor a more difficult experience than normal weight women. Upon examination, uterine muscles from the obese group performed poorly and contracted less well than matched samples from normal weight group. It was that less calcium was able to enter the uterine cells of the obese women to support uterus muscles in contracting during labor.

Researchers believe that it could be high levels of cholesterol in obese women's bloodstream that is disrupting cell membranes and signaling pathways, including calcium entry.

Pregnancies among overweight women are considered high risk pregnancies and these women should have good antenatal care.