Global Warming and Quality of Eggs
Adapted from Impact of ambient temperature on ovarian reserve, published in October 2021 issue of Fertility and Sterility.
Climate change is widely recognized as the greatest global threat of the 21st century.
By 2070, the risk of exposure to extreme heat for the average United States citizen is expected to increase four to sixfold relative to the late 20th century.
Little is known regarding the relationship between ambient temperature and fertility in humans. Demographic studies suggest that hot weather causes a significant decline in birth rates 8–10 months later, yet the causes of this association are unclear.
A study conducted by Massachusetts General Hospital Fertility Center was designed to examine the association between ambient temperature and antral follicle counts (AFC). Antral follicle count is one of the most reliable measures of ovarian reserve (how likely ovaries can produce biologically "perfect" eggs).
The study analyzed the ovarian AFC of 631 women by transvaginal ultrasonography. No fertility medications were used in the cycle before the antral follicle ultrasound scan.
The median AFC was 12 with a range of 1–30. Mean AFC varied by age, education level, infertility diagnosis, and year and month of AFC assessment.
There was a persistent, negative, linear association between temperature and AFC across the entire range of temperatures observed in the study. A 1°C increase in average maximum temperature during the 90 days before ovarian reserve testing was associated with a −1.6% lower 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.
Women experiencing higher than average temperatures in the winter and early spring may be more likely to suffer from uncompensated heat stress because the body is unable to maintain a steady thermal state, possibly leading to worse health outcomes, such as impaired follicular growth.
In conclusion, the study showed that 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.