Association between adverse nutrition status by BMI and increased time-to-pregnancy in planed pregnancy couples: A cohort study in Guangzhou, China

Abstract

Abstract Background This study addresses China's low fertility and aging issues by examining the impact of overweight and obesity on fertility. Given inconsistent results in previous research, mostly focused on females, our study targets couples in Guangzhou. We investigate the relationship between Body Mass Index (BMI) and Time to Pregnancy (TTP) to provide evidence-based strategies for enhancing reproductive outcomes in China. Methods This cohort study, utilizing the National Free Pre-pregnancy Checkups Project (NFPCP), employs a Cox regression model to assess the correlation between different BMI categories and TTP. Heatmaps are utilized to investigate the association between various BMI combinations of couples and TTP. Additionally, we use Restricted Cubic Spline (RCS) curves to explore the non-linear relationship between male and female BMI and TTP. Results The results showed that overweight and obese females (fecundability ratios (FR)0.783, 95%CI 0.644,0.954) and males (FR0.857, 95%CI 0.758,0.970) had longer TTP compared with normal weight, regardless of controlled covariates, while underweight females and males also had longer TTP, but the difference was not statistically significant (P > 0.05). Among all BMI combinations, couples in the overweight and obese groups had the lowest fertility, with a 34% decrease in fertility (TTP) compared to couples in the normal BMI combination (FR0.66; 95% CI 0.50,0.85). After adjusting for all covariates in the RCS model, female BMI surpassing 23.65 and male BMI within the range of 23.4 to 29.4continued to indicate a decrease in fertility (FR less than 1) with statistical significance. Conclusions: Elevated BMI, both in females and males, emerges as a significant predictor of prolonged TTP.