The Impact of Aging on Women's Fertility

As societal norms evolve, an increasing number of women are choosing to delay motherhood. In Sweden, this trend is evident as mothers are becoming older when they have their first child. However, age remains a crucial factor influencing a woman's ability to conceive using her own eggs.

The decline in fertility associated with aging can be attributed to two primary factors: a reduced number of eggs and a decline in egg quality. While individual variations exist, fertility typically begins to decrease after the age of 35, with a more pronounced drop occurring after the age of 38.

At the age of 25, a woman's fertility peaks. Nevertheless, even at this optimal age, only about one in three eggs released from the ovaries possesses sufficient quality to develop into a viable pregnancy, and this ratio diminishes with age. As women grow older, the quality of their eggs declines, resulting in an increased risk of chromosomal abnormalities. Furthermore, older eggs exhibit a diminished capacity to generate the energy necessary for normal embryonic development.

In comparison to other species, human females are among the least fertile. For instance, nearly all eggs in the ovaries of mice and rats are capable of successful fertilization. Women, on the other hand, have a limited number of viable eggs, and their reproductive years conclude with menopause. The ovaries are typically the first organs to show signs of aging in women.

The reasons for this unique biological setup remain unclear, but there are theories suggesting that evolution has molded human reproductive capabilities to ensure a manageable number of offspring, unlike species such as rodents that can sustain larger litters.

As more individuals seek medical assistance to conceive, the importance of age, particularly for women undergoing in vitro fertilization (IVF), becomes even more pronounced. While male age is also a factor, its impact is significantly less than that of female age, given that sperm cells are continuously produced in the testes and do not age in the same manner as eggs do.

Additionally, several lifestyle and environmental factors adversely affect both male and female fertility. Smoking, obesity, and exposure to pollutants and hormone-disrupting substances can all diminish reproductive capabilities. Medical interventions, such as chemotherapy, can further compromise fertility.

This information has been compiled with the assistance of Pauliina Damdimopoulou, an associate professor of endocrine physiology at the Karolinska Institute.