Women who are underweight before they become pregnant are at heightened risk for suffering a miscarriage in the first trimester, a UK study shows, but taking vitamin supplements and eating fresh fruit and vegetables can reduce the risk.

Although there are several well-established risk factors for miscarriage, including older age of the mother, a history of miscarriage, and infertility, the cause of the majority of miscarriages is not fully understood.

In an attempt to uncover additional risk factors, Dr. Noreen Maconochie and colleagues from the London School of Hygiene and Tropical Medicine conducted a “case-control” study. Cases comprised 603 women whose most recent pregnancy ended in miscarriage at less than 13 weeks gestation, while controls comprised 6,116 women whose most recent pregnancy had progressed beyond the first trimester.

Women having a low pre-pregnancy body mass index (BMI less than 18.5) had a 72 percent higher likelihood of suffering a miscarriage in the first trimester, the authors found. There was no evidence that being overweight or obese played a role in miscarriage.

The BMI is the ratio between height and weight. A BMI between 18.5 and 24.9 is considered normal; 25.0 to 29.9 overweight; and BMI of 30.0 or greater is considered obese.

The team also found that taking vitamin supplements, particularly those containing folic acid or iron, during early pregnancy cuts the risk of miscarriage by about 50 percent. Eating fresh fruit and vegetables daily or on most days was also found to lower the risk of miscarriage. And chocolate lovers rejoice, eating chocolate was associated with decreased odds of miscarriage.

Women who were not married or living with a partner or had changed partners had a significantly increased risk of miscarriage, as did those who had a previous pregnancy terminated and those who had trouble getting pregnant.

Women who said their pregnancy was “planned” had a 40 percent reduced odds of miscarriage. Feelings of emotional well-being were also associated with reduced risk.

All types of assisted reproduction increased the odds of miscarriage, but the greatest risk seemed to result from intrauterine insemination or artificial insemination.

Women who had morning sickness were almost 70 percent less likely to miscarry, a finding that confirms the “widely held belief that morning sickness is an indicator that the pregnancy is progressing well,” according to a statement from the researchers.

“Our results,” Maconochie noted in comments to Reuters Health, “confirm that advice to encourage a healthy diet, reduce stress and promote emotional well-being might help women in early pregnancy (or planning a pregnancy) reduce their risk of miscarriage.”

“This was an exploratory study,” she emphasized, and “findings of increased risk associated with previous termination, stress, change of partner and low pre-pregnancy weight are noteworthy, and we recommend further work to confirm these findings in other study populations.”

SOURCE: BJOG: An International Journal of Obstetrics and Gynecology 2006.