Impact of ambient temperature on ovarian reserve

Abstract

Objective: To examine the association between ambient temperature and antral follicle count (AFC), a standard measure of ovarian reserve.

Design: Prospective cohort study.

Setting: Fertility center at an academic hospital in the northeastern United States.

Patient(s): 631 women attending the Massachusetts General Hospital Fertility Center (2005-2015) who participated in the Environment and Reproductive Health Study.

Intervention(s): Daily temperature at the women's residential address was estimated for the 90 days before their antral follicle scan using a spatially refined gridded climate data set. We evaluated the associations between temperature and AFC using Poisson regression with robust standard errors, adjusting for relative humidity, fine particulate matter exposure, age, education, smoking status, year and month of AFC, and diagnosis of diminished ovarian reserve and ovulation disorders.

Main outcome measure(s): Antral follicle count as measured with transvaginal ultrasonography.

Result(s): A 1°C increase in average maximum temperature during the 90 days before ovarian reserve testing was associated with a -1.6% (95% confidence interval [CI], -2.8, -0.4) lower AFC. Associations remained negative, but were attenuated, for average maximum temperature exposure in the 30 days (-0.9%, 95% CI, -1.8, 0.1) and 14 days (-0.8%, 95% CI, -1.6, 0.0) before AFC. The negative association between average maximum temperature and AFC was stronger in November through June than during the summer months, suggesting that timing of heat exposure and acclimatization to heat may be important factors to consider in future research.

Conclusion(s): Exposure to higher temperatures was associated with lower ovarian reserve. These results raise concern that rising ambient temperatures worldwide may result in accelerated reproductive aging among women.

Keywords: Climate change; environment; fecundity; fertility; ovarian reserve; temperature.

Figure 1.

Overview of the timeframe of follicular development in humans and the relevant exposure windows evaluated for the association between ambient temperature and antral follicle count.

Figure 2.

Association between average maximum temperature in the three months prior to scan and antral follicle counts (AFC) among 631 women in the EARTH Study fit with a restricted cubic spline. Models were adjusted for average relative humidity (continuous) and PM_2.5 exposure (continuous) in 3 months prior to AFC, age (continuous), education (<college vs. ≥college), smoking status (ever vs. never), year of AFC (continuous), month of AFC (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec), and diagnosis of diminished ovarian reserve and ovulation disorders.