Pre-pregnancy body mass index and time to pregnancy among couples pregnant within a year: A China cohort study

Yuhang Fang; Jun Liu; Yanyan Mao; Yang He; Min Li; Liu Yang; Qianxi Zhu; Qi Tong; Weijin Zhou

doi:10.1371/journal.pone.0231751

Pre-pregnancy body mass index and time to pregnancy among couples pregnant within a year: A China cohort study

PLoS One. 2020 Apr 23;15(4):e0231751. doi: 10.1371/journal.pone.0231751. eCollection 2020.

Authors

Yuhang Fang^{1

2}, Jun Liu³, Yanyan Mao^{1

2}, Yang He³, Min Li², Liu Yang³, Qianxi Zhu², Qi Tong³, Weijin Zhou²

Affiliations

¹ School of Public Health, Fudan University, Shanghai, China.
² NHC Key Lab. of Reproduction Regulation, Shanghai Institute of Planned Parenthood Research, Fudan University, Shanghai, China.
³ NHC Key Laboratory of Birth Defects and Reproductive Health (Chongqing Population and Family Planning Science and Technology Research Institute), Chongqing, China.

Abstract

Background: Extreme pre-pregnancy body mass index (BMI) values have been associated with reduced fecundability and prolonged time to pregnancy in previous studies. However, the effect in fertile couples is unclear.

Objectives: This study aimed to evaluate the association between pre-pregnancy BMI and fecundability, measured as time to pregnancy (TTP), among couples that achieved pregnancy within 1 year.

Methods: This was a retrospective cohort study of 50,927 couples wishing to conceive, enrolled in the National Free Preconception Health Examination Project (NFPHEP) in Chongqing, China, during 2012-2016. Participants' weight and height were measured by NFPHEP-trained preconception guidance physicians. TTP measured in months was used to determine subfecundity (TTP >6 months). The strength of association between BMI and TTP/subfecundity was measured with fecundability odds ratios (FOR)/odds ratios (OR) and their corresponding 95% confidence intervals (CI), calculated with Cox and logistic regression analysis. We used restricted cubic spline regression (RCS) to test the observed FOR trends.

Results: Compared to women with normal BMI, women with pre-pregnancy overweight/obesity had longer TTP (FOR = 0.96, 95% CI: 0.94-0.99) and increased risk of subfecundity (OR = 1.08, 95% CI: 1.00-1.17). There was no association between TTP and male BMI. RCS trends varied when data were stratified by male pre-pregnancy BMI, with the greatest change detected in pre-pregnancy underweight men.

Conclusions: Pre-pregnancy overweight/obesity was associated with longer TTP and subfecundity among women who became pregnant within 1 year; this effect was likely mediated by their partners' pre-pregnancy BMI. These findings indicate that BMI could affect fecundability, independently of affecting the risk of sterility. Advice on weight management and maintaining healthy weight should be included in couples' preconception guidance.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Aged
Body Mass Index*
China
Cohort Studies
Female
Humans
Infertility / etiology
Male
Middle Aged
Obesity / complications
Obesity / epidemiology*
Pregnancy
Retrospective Studies
Time-to-Pregnancy / physiology*
Young Adult

Grants and funding

This study was supported by Innovation-oriented Science and Technology Grant from NHC Key Laboratory of Reproduction Regulation (No. CX2017-04); grant from ChongQing Science And Technology Bureau (No. cstc2017shmsA130102, No. cstc2017jxjl10001); grant from Health Commission of Chongqing province (No. 2017ZDXM015); grant from NHC Key Laboratory of Reproduction Regulation (No. 2017KF04). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.