Scientists have discovered that the problems commonly experienced by obese women while giving birth are due to failure of the muscles in the uterus.
Nearly one in five overweight women have to give birth by emergency Caesarean section and, according to researchers from the University of Liverpool, obese women are 3.5 times more likely to require a Caesarean for slow labour than women of normal weight.
Their study of 4,000 pregnant women, which is published in the British Journal of Obstetrics and Gynaecology, suggests that obesity may impair the ability of the uterus to contract sufficiently in order to dilate the cervix and deliver the baby naturally.
In addition, the research found that obese women who succeed in a natural birth also suffer more complications.
More than twice as many (six per cent) experience excessive bleeding following delivery, probably also due to poor uterine activity as the womb is unable to contract sufficiently to clamp off the blood vessels broken following delivery of the placenta.
Professor Sue Wray said that high levels of cholesterol in an obese woman's bloodstream could be preventing sufficient levels of calcium from entering the muscles of the uterus.
Dr Siobhan Quenby from the University of Liverpool's obstetrics department commented: "In the meantime it is vital pre-pregnancy advice and counselling is available to women about the implications of weight on childbirth.
"Pregnancies among overweight women must be classified as high risk pregnancies and appropriate antenatal care should be provided so they receive the optimum care during maternity."
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