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.
The researchers found that women who separated from their partners after becoming pregnant increased their odds of a miscarriage by more than 60 percent and unmarried women or those living with a partner were also at a greater risk than those who "planned" their pregnancies.
In fact planned pregnancies were 40% less likely to miscarry than those conceptions which were accidental, but those who took more than a year to conceive were twice as likely to miscarry as those who had conceived within three months.
The study leader, Noreen Maconochie, a senior lecturer in epidemiology and medical statistics, says the findings which relate in particular to low pre-pregnancy weight, previous termination, stress and change of partner, are worthy of more research.
Maconochie also says advice to encourage a healthy diet and to try and reduce stress and promote emotional well-being might help women in early pregnancy, or those planning a pregnancy, reduce their risk of miscarriage.
The study is published in the British Journal of Obstetrics and Gynaecology.