Influence of BMI on risk of miscarriage after single blastocyst transfer

BACKGROUND: Debate exists regarding the effect of raised BMI on the outcome of pregnancies after assisted reproduction technology. We assessed the effect of BMI on the risk of miscarriage in women conceiving following single blastocyst transfer (SBT) after controlling for confounding factors. METHODS: Fresh and cryo-thawed cycles of SBT that resulted in a pregnancy between January 2006 and March 2010 were included. Patients with BMI < 18.5 kg/m(2) or older than 40 years were excluded. Patients were grouped according to their BMI at the start of treatment cycle. The main outcome measure was the miscarriage rate before 23 weeks gestation. Confounding variables examined included female age, duration and cause of infertility, previous miscarriage, smoking status and quality of blastocyst replaced. RESULTS: A total of 413 women conceived following SBT in fresh (n = 325) or cryo-thawed (n = 88) IVF cycles, of whom 244 had a normal BMI (18.5-24.9) and 169 had a raised BMI of >= 25. Overall, 27% (113/413) of women miscarried before 23 weeks gestation. Women with a BMI of >= 25 had more than double the risk of miscarriage compared with women who had normal BMI [38 versus 20%, odds ratio (OR): 2.4, 95% confidence interval (CI) 1.6-3.8, P < 0.001, respectively]. After adjusting for confounding variables, having a BMI of >= 25 significantly increased the risk of clinical miscarriage before 23 weeks gestation in both fresh (adjusted OR = 2.7, 95% CI 1.5-4.9, P = 0.001) and cryo-thawed IVF cycles (OR = 6.8, 95% CI 1.5-31.1, P = 0.012). CONCLUSIONS: Raised BMI is independently associated with higher miscarriage rate after IVF treatment.