A new study has shown that underweight and overweight women are at a significantly higher risk of experiencing recurrent miscarriages compared to those of average weight.

A research team led by the University of Southampton assessed the link between women's lifestyle and risk of recurrent pregnancy loss, defined as women having two or more consecutive early miscarriages. The systematic review and meta-analysis study has been published in the journal Scientific Reports.

Miscarriage is the most common complication of early pregnancy, affecting between 15% and 20% of all pregnancies. Recurrent pregnancy loss is a complex disease and although often attributed to numerous medical factors and lifestyle influences, the cause is deemed "unexplained" in around 50% of cases.

The results of this latest study found that there are higher occurrences of successive miscarriages in mothers who are underweight (having a Body Mass Index score of less than 18.5), overweight (having a BMI between 25 and 30) and obese (having a BMI above 30).

The study's first author, Dr. Bonnie Ng, MRC Fellow in Clinical and Experimental Sciences at the University of Southampton, said, "Our study included 16 studies and showed that being underweight or overweight significantly increases the risk of two consecutive pregnancy losses. For those with BMI greater than 25 and 30, their risk of suffering a further miscarriage increases by 20% and 70% respectively."

The research team also set out to assess the impact of factors such as smoking and consumption of alcohol and caffeine. However they were unable to establish conclusively whether these have any impact or not due to inconsistencies of the results from a small number of studies and heterogeneity in women taking part in them.

Co-author Dr. George Cherian, specialist trainee in obstetrics and gynecology at Princess Anne Hospital, Southampton, said, "While our study did not find any associations between recurrent pregnancy loss and lifestyle parameters such as smoking, alcohol and caffeine intake, further large-scale studies are required to clarify this."

Whilst recognizing that more observational and clinical research is needed to establish the full extent of lifestyle choices, the authors conclude that weight is a risk factor that can be modified to reduce the risk.

"Our findings suggest that having an abnormal BMI exacerbates a woman's risk of suffering from repeated miscarriages, and so clinicians really need to focus on helping women manage this risk factor' concluded Ying Cheong, professor of reproductive medicine at the University of Southampton and senior author on the paper.