Women using assisted reproductive technology (ART) to conceive have a higher rate of miscarriage if they are overweight, say a group of UK scientists.
Speaking today at the 26th annual conference of the European Society of Human Reproduction and Embryology (ESHRE) in Rome, Italy, the group say the information from the study should be included in the counselling provided for patients before undergoing ART.
The group performed single blastocyst transfer (SBT) on 323 women over a four year period from January 2006 to December 2009. They categorized the women into two groups: those with a 'normal' range body mass index (BMI) of 18.5 - 24.9 (184 women), and those with higher BMI of above 25 (139 women). Of the latter group, 19 women were clinically obese, with a BMI of 30 or over.
The scientists found that there was a higher rate of miscarriage among the overweight and obese women: one in three obese women, compared to one in five women of normal weight. After adjusting for confounding variables, such as age, miscarriage history, duration of infertility and smoking habits, the researchers showed that being overweight or obese doubled the risk of miscarriage.
'Although there is evidence that miscarriage rates are higher in overweight women who conceive spontaneously, there were conflicting views about the effect of increased weight on the outcome of pregnancies occurring after IVF and ICSI (intracytoplasmic sperm injection). The difficulty of interpreting the studies to date is that they are heterogeneous', said lead researcher, Dr Vivien Rittenberg, from Guy's and St Thomas' Hospital NHS Foundation Trust, London. 'Our study differs in that we transferred only one embryo at a specific stage of development, and were therefore able to provide clear evidence of the deleterious effect of being overweight on the chances of miscarriage'.
Women hoping to conceive are already warned of the other problems caused by obesity in pregnancy, including difficulty to conceive, high blood pressure, pre-eclampsia, diabetes, premature delivery and post-partum bleeding.
Dr Rittenberg emphasised that the work shows for the first time the wider health issues of undergoing ART whilst being overweight, and hopes that the advice given to women will be to 'lose weight not only if they are obese but also if overweight', and this should be advice 'independent of spontaneous conception or fertility treatments'.
Fertility problems affect one in six couples worldwide at least once in their lives, with cases linked to physiological causes as well as lifestyle factors. Many couples seek resolution in ART, with 54 per cent of the cycles worldwide being carried out in Europe.