Overweight women urged to slim down before trying for a baby to avoid birth defects
Experts have urged overweight women trying to have a baby to slim down before sex.
The call comes after new research showed a rising risk of serious birth defects as the body mass index (BMI) of mothers increased.
Women of reproductive age should be encouraged to "adopt a healthy lifestyle and to obtain a normal body weight before conception", said the authors.
It was already known being obese heightens the chances of a woman giving birth to a child with malformations that can affect physical appearance or the functioning of nerves and organs.
But the new study revealed a sliding scale of risk that went up as weight increased.
Researchers analysed data on more than 1.2 million live singleton births in Sweden, recorded between 2001 and 2014. Among normal weight mothers with a BMI of 18.5 to 24, a total of 3.4pc had children with birth defects.
Overweight mothers with a BMI of 25 to 29 had a birth defect risk of 3.5pc. The rate of birth defects went up to 3.8pc for obese women with a BMI of 30 to 34, and rose to 4.2pc and 4.7pc for higher categories of obesity. BMI is obtained by dividing weight in kilograms by height in centimetres squared. It takes account of different stature when assessing weight.
The scientists, led by Martina Persson, from Sweden's Karolinska Institute, wrote in the 'British Medical Journal': "Risks of any major congenital malformation progressively increased with maternal overweight and increasing severity of obesity."