Maternal preconception body mass index and time-to-pregnancy in Shanghai Women, China

Previous studies suggested an association between female fertility and body size, but most of these studies were from Western countries and focused mainly on obesity. This study investigated the association between preconception body mass index (BMI) and time to pregnancy (TTP) in women planning to conceive from Shanghai, China. A total of 1,182 women aged 24-46 years were recruited from the Shanghai Birth Cohort between 2013 and 2015 and were followed up for 12 months. Preconception BMI was categorized as underweight, normal weight, and overweight/obesity according to the Chinese classification of BMI. Fecundability (FOR) and infertility (IOR) odds ratios were estimated using Cox (n = 1,092) and Logistic (n = 820) regression models, respectively. We found no differences in fecundability between underweight and overweight/obese women and normal-weight women. Furthermore, underweight and overweight/obese women did not have a higher risk of infertility compared with normal-weight women. Our findings suggest that non-optimal preconception BMI does not appear to influence female fecundability and infertility in Chinese women. These results should be interpreted with caution as they may be applicable only to women with demographic and anthropometric characteristics similar to our study population. Our findings need to be confirmed in other populations.