Mothers who gain or lose a great deal of weight between pregnancies could be putting themselves and their babies at risk, experts have said.

Even quite small changes in body mass index (BMI), of one or two units, between pregnancies are enough to have effects, say Jennifer Walsh and Deirdre Murphy, two obstetricians from Dublin. An increase of this size has been linked with a doubling of the risks of high blood pressure, preeclampsia, and having a large baby. Greater increases in weight between pregnancies add to the risk of stillbirth and other complications, they say in an editorial in the British Medical Journal.

On the other hand, they add, women losing a lot of weight run a greater risk of having premature babies, or babies of low birth-weight.

The message is that women should try to maintain a healthy weight before, during and after pregnancy – and to be the same weight at any subsequent pregnancies.

Dr Walsh, a specialist registrar in obstetrics and gynaecology at Coombe Women’s Hospital in Dublin, and Professor Murphy, Professor of Obstetrics at Trinity College Dublin, say: “Women of reproductive age are bombarded with messages about diet, weight and body image.

“There is growing concern on the one hand about an epidemic of obesity, and on the other about a culture that promotes ‘size zero’ as desirable, irrespective of a woman’s natural build.

“Pregnancy is one of the most nutritionally demanding periods of a woman’s life, with an adequate supply of nutrients essential to support foetal wellbeing and growth.

“With at least half of all pregnancies unplanned, women need to be aware of the implications of their weight for pregnancy, birth and the health of their babies.

“We should ensure that women of low body mass index attain a healthy weight before conception to reduce the risk of preterm birth and low infant birth-weight.

“We should also counsel women with a history of previous preterm birth to maintain a healthy weight to prevent recurrence.”

The authors cited studies on the effects of weight gain and weight loss. The first, a Swedish study, followed 207,534 women from 1992 to 2001 to examine the link between changes in body mass index and the impact on a baby and mother’s health.

The second, which was published last year in the American Journal of Obstetrics and Gynaecology,found that women whose BMI fell by five or more units between pregnancies had a higher risk of premature birth than women whose weight remained stable or increased. The effect was heightened among women who had already experienced one premature birth.

Tam Fry, board member of the National Obesity Forum, said: “I think these doctors are absolutely right.

“It’s fundamental that we teach girls at school not only to lose weight for their own health but also because of the risks to their child of entering motherhood being overweight.”

Being overweight was associated with polycystic ovary syndrome, which could result in difficulty conceiving, he said.

“There is a known association between overweight and obese parents and the likelihood of a child being overweight themselves.

“Women should be aiming for a normal weight before they have their second child.

“Women also go the other way and starve themselves to plummet to a goal weight. They try to get down to a certain weight, and that is also wrong.”

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