Thin women hoping to conceive have been warned that their chances of miscarrying in the early stages of pregnancy are significantly increased.

Research conducted by the London School of Hygiene & Tropical Medicine has found that women with a low body mass index before becoming pregnant are 72 per cent more likely to miscarry in the first three months of pregnancy.

To counteract this increased likelihood of losing a baby, however, thinner women are advised to take supplements and to eat fresh fruit and vegetables.

It is thought that around 250,000 women suffer a miscarriage every year in the UK and scientists have pontificated for years and years over the various theories as to why this tragic misfortune strikes some and not others.

Generally accepted is the fact that older mothers, women with a history of miscarriage and women with fertility difficulties are more at risk than most. Aside from these primary factors very little has been set in stone, but the new report insists that there is strong evidence that body mass index and diet are crucial factors.

While underweight women are 72 per cent more likely to miscarry in the first trimester, taking vitamin supplements reduces this risk by 50 per cent, according to the study. The scientists believe that folic acid and iron are particularly beneficial in reducing the chances of a miscarriage.

Significantly, consumption of fresh fruit and vegetables also halves the chances of miscarriage, but many women will be more interested in the indication that chocolate is hugely favourable too.

Aside from diet, living arrangements also appear to have an impact on a woman's chances of miscarrying. A woman who has changed partners after becoming pregnant, for instance, has a 60 per cent higher risk of suffering a miscarriage.

Morning sickness, meanwhile, appears to be a sign that the pregnancy is progressing well, in that women who suffered nausea and sickness in the first trimester were around 70 per cent less likely to miscarry than those who escaped these symptoms.

The study has been published in the online edition of BJOG: An International Journal of Obstetrics and Gynaecology.

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