Researchers at the London School of Hygiene and Tropical Medicine in England have found that being very thin and underweight might increase the risk of women miscarrying during pregnancy.
The researchers say really thin women are 72% more likely to miscarry in the first three months of pregnancy than women of normal weight.
According to experts, underweight means those women with a body mass index of under 18.5.
They reached this conclusion after conducting a study of 603 women aged 18 to 55 who had miscarried within three months of getting pregnant and another 6,000 whose pregnancies continued beyond 12 weeks.
They found that women who suffered from nausea and sickness in the first 12 weeks were almost 70% less likely to miscarry, and the more severe the sickness, the better the odds of the pregnancy continuing.
The new research which looked at the diet and lifestyles of the women, also suggests a diet which includes fruit, vegetables, and chocolate, helped reduce the risk of miscarriage.
It was also found that women who took vitamin supplements, in particular folic acid or iron and multivitamins, during early pregnancy reduced their risk by around 50%.
It is estimated that one in five pregnancies in the UK will end in miscarriage, which equates to around 250,000 women every year.
Despite the well known risk factors, such as increased maternal age, a previous history of miscarriage, and infertility, the causes of the majority of miscarriages are unclear and suspected risk factors, such as alcohol consumption, smoking and caffeine intake, are unconfirmed.