Ambient temperature and fecundity in 2.4 million couples

Jing Cai; Yang Shen; Jing Dong; Yue Niu; Yixiang Zhu; Cheng He; Shuyan Shi; Huimin Li; Qiaomei Wang; Haiping Shen; Yiping Zhang; Donghai Yan; Michelle L Bell; Xu Ma; Haidong Kan; Yuan He

doi:10.59717/j.xinn-med.2025.100139

The Innovation Medicine > 2025 Vol. 3 > No. 3 > 100139

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Ambient temperature and fecundity in 2.4 million couples

1.
School of Public Health, Key Lab of Public Health Safety of the Ministry of Education and NHC Key Lab of Health Technology Assessment, Fudan University, Shanghai 200032, China
2.
IRDR ICoE on Risk Interconnectivity and Governance on Weather/Climate Extremes Impact and Public Health, Fudan University, Shanghai 200032, China
3.
National Research Institute for Family Planning, Beijing 100081, China
4.
National Human Genetic Resources Center, Beijing 101199, China
5.
Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China
6.
Institute of Epidemiology, Helmholtz Zentrum München—German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg D-85764, Germany
7.
Department of Maternal and Child Health, National Health Commission of the People’s Republic of China, Beijing 100088, China
8.
School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, USA
9.
Children’s Hospital of Fudan University, National Children’s Medical Center, Shanghai 200127, China
10.
These authors contributed equally

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Corresponding authors: jingcai@fudan.edu.cn. (J.C.); maxu_fg@nrifp.org.cn (X.M.); kanh@fudan.edu.cn (H.K.); heyuan8506@126.com (Y.H.)
Received Date: February 15, 2025

Accepted Date: June 20, 2025

Published Online: July 02, 2025

The Innovation Medicine 3(3), https://doi.org/10.59717/j.xinn-med.2025.100139 | Cite this article

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PUBLIC SUMMARY

PUBLIC SUMMARY
1. Exposure to higher temperatures were associated with reduced fecundity and longer time to pregnancy.
  
  Exposure-response relationships exhibited a monotonic manner.
  
  Decline in fecundity associated with rising temperatures was stronger in the East, South, and North regions.
  
  The associations were stronger in couples where the woman was overweight/obese or exposed to second-hand smoke.
  
  The associations were stronger in couples where the man was overweight/obese or consumed alcohol.

ABSTRACT

ABSTRACT

Climate change may affect fertility; however, associations between ambient temperature and human fecundity remain understudied. We assessed the relationship between temperature and fecundity in 2,443,879 reproductive-age couples from 350 cities across China, with follow-up every 3 months until conception or for up to 1 year. We used Cox regression models to evaluate associations of 1-year, 6-month, and 3-month average temperature exposures preceding conception or censoring with fecundability odds ratios (FORs). Accelerated failure time and multivariate linear regression models were applied to examine associations between temperature and time to pregnancy (TTP). During the one-year follow-up, 2,038,378 (83.4%) couples conceived. Higher temperatures were associated with reduced fecundity and extended TTP, with monotonic exposure-response curves observed. Specifically, a 1°C increase in 1-year average temperature was associated with a 4.2% decrease in fecundity (FOR=0.958, 95% confidence interval [CI]: 0.957, 0.959). The corresponding absolute probability of pregnancy within 1 year decreased by 1.35% (absolute risk difference=–1.35%, 95% CI: –1.41%, –1.26%). Each 1°C increase in annual average temperature was associated with a 2.5% increase in median TTP for all couples (time ratio=1.025, 95% CI: 1.024, 1.025). Among couples who conceived within 1 year, TTP was prolonged by 1.60% (95% CI: 1.55%, 1.65%). Smaller FOR estimates, indicating reduced fecundity, were observed in the East, South, and North regions; in tropical and temperate monsoon zones; and among couples where either partner was overweight/obese, woman was attempting her first pregnancy or exposed to second-hand smoke, or man consumed alcohol. Increased temperatures may adversely impact fecundity by prolonging TTP, highlighting the need for heat mitigation strategies.

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Cai J., Shen Y., Dong J., et al. (2025). Ambient temperature and fecundity in 2.4 million couples. The Innovation Medicine 3:100139. https://doi.org/10.59717/j.xinn-med.2025.100139

Cai J., Shen Y., Dong J., et al. (2025). Ambient temperature and fecundity in 2.4 million couples. The Innovation Medicine 3:100139. https://doi.org/10.59717/j.xinn-med.2025.100139

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