A UK population-based study of risk factors for first-trimester miscarriage confirms the importance of established risk factors, such as maternal age, and finds no support for popular beliefs about the effects of caffeine and working during pregnancy.

In the February issue of the British Journal of Obstetrics and Gynaecology, Dr. Noreen Maconochie and colleagues at the London School of Hygiene and Tropical Medicine, note that the reason for most miscarriages is not wholly understood, and many risk factors remain controversial or unconfirmed.

Well-established risk factors for miscarriage include older maternal age and a history of miscarriage and infertility. Several behavioral and social risk factors have been reported to increase the risk of miscarriage, but evidence is scant.

To investigate further, the researchers surveyed 603 women between 18 and 55 years old whose most recent pregnancy ended in miscarriage after less than 13 weeks. As a comparison group, they also included 6116 women whose pregnancies had gone beyond 12 weeks.

The established risk factors mentioned previously were confirmed, and additional risk factors were identified. These included having fertility treatments to assist with conception; having a low body weight before pregnancy; drinking alcohol regularly or in large amounts; feeling stressed-out; having an older man father the pregnancy; and having changed a partner.

Factors associated with a reduced risk were previously delivering a child; delivering a live infant; being nauseous during pregnancy; taking vitamin supplements; and eating fresh fruits and vegetables daily. Notably, women who experienced nausea and vomiting were almost 70 percent less likely to miscarry.

The researchers did not find any association between miscarriage and caffeine consumption, smoking, and moderate or occasional alcohol consumption. There was also no apparent association with educational level, socioeconomic circumstances or working during pregnancy.

The investigators call for further studies, but conclude that the best advice that may help pregnant women reduce their risk of miscarriage is to encourage a healthy diet, reduce stress and promote emotional well-being.

SOURCE: British Journal of Obstetrics and Gynaecology, February, 2007.