The National Institute for Health and Clinical Excellence (NICE) has issued a health warning amid fears of obesity among pregnant women.

The health watchdog says that obesity levels among pregnant women have reached epidemic levels, putting the health of their babies at risk.

It is urging women to get to a healthy weight before conceiving and with evidence suggesting that some 50% of women of childbearing age are obese or overweight, NICE wants to cut through some of the conflicting advice about health during pregnancy.

NICE advises women against “eating for two” when pregnant and to discuss weight and exercise before, during and after pregnancy.

Obesity during pregnancy can increase the risk of developing complications such as pre-eclampsia, gestational diabetes, miscarriage and stillbirth.

NICE public health director Mike Kelly said: “Women should understand that weight loss after birth takes time, and physical activity and gradual weight loss will not affect their ability to breastfeed.

“Losing weight gradually can actually help women maintain a healthy weight in the long term.”

NICE says women with a body mass index of more than 30 should be encouraged to lose weight before they become pregnant.

Professor Lucilla Poston, from King's College, London, who helped develop the guidance, said: “There's been an exponential increase in obesity among pregnant women. It's very worrying, as there are so many potential risks for the mother and her baby.”

The National Childbirth Trust welcomed the move to bring clarity to the issue amid a lot of conflicting advice about exercise.