Ambient temperature and fecundity in 2.4 million couples

<p>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.</p>