Women whose body mass index was low — below 18.5 — when they conceived were much more likely to have a miscarriage in the first three months of pregnancy. But being overweight appeared to have adverse consequences on a pregnancy.

A study commissioned by the Miscarriage Association suggests that taking vitamin supplements during the first weeks of pregnancy halved the odds of a miscarriage as did eating fresh fruit and vegetables. Even eating chocolate reduced the risk slightly. Other factors that increased the chance of a successful pregnancy included a planned conception and marriage, said the study, which is published online in the British Journal of Obstetrics and Gynaecology today.

Every year an estimated 250,000 women miscarry, but while there are a number of well-established risk factors, including increased maternal age, high alcohol consumption or fertility problems, the exact cause of most miscarriages is unknown.

Noreen Maconochie and Pat Doyle, of the London School of Hygiene and Tropical Medicine, studied 603 women aged 18 to 55 who had suffered a miscarriage in the first trimester (less than 13 weeks’ gestation) and compared their lifestyles with those of more than 6,000 women whose pregnancies progressed beyond 12 weeks.

They found that women who had a BMI of less than 18.5 when they conceived were 72 per cent more likely to miscarry in the first trimester. Those with what is considered a normal BMI score of 18.5 to 25, and those above were not found to increase their risk of miscarriage.

Ms Maconochie, the lead author, said yesterday: “Our study confirms the findings of previous studies, which suggest that following a healthy diet, reducing stress and looking after your emotional wellbeing may all play a role in helping women in early pregnancy, or planning a pregnancy, to reduce their risk of miscarriage.”

The findings suggested that if a woman was not married or living with a partner, her risk of miscarriage was higher. If she changed partner during pregnancy, her odds increased by 60 per cent.

The odds of a miscarriage increased by 60 per cent for women who had a history of abortion and 41 per cent for those who had fertility problems. All types of assisted reproduction were associated with increased odds, but the ratios were highest among pregnancies that resulted from intrauterine insemination or artificial insemination.

The Miscarriage Association said: “These findings are really very interesting and surprising. When it comes to weight most of the anecdotal evidence had previously been around women who were overweight.”

Preparing for a better pregnancy

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