fertility

Fertility is the ability of individuals or populations to reproduce. At the individual level, it refers to the biological capacity to conceive and bear offspring, which depends on the functioning of the reproductive system, hormonal regulation, and gamete health. At the population level, fertility is often described by measures such as the total fertility rate, which estimates the average number of children a woman would have over her lifetime given current age-specific fertility patterns. Fertility is influenced by biological, environmental, social, and economic factors.

In humans, female fertility depends on regular ovulation, the health of the fallopian tubes, and the uterine environment, while male fertility depends on adequate sperm production, motility, and morphology. Fertility generally declines with age, especially for women after their mid-30s, due to diminishing oocyte quality and quantity. Male fertility can also decline with age, though often later and more gradually. Lifestyle factors such as nutrition, body weight, smoking, alcohol use, and exposure to environmental toxins can affect both sexes.

Infertility affects a share of couples and is defined clinically as the failure to achieve a pregnancy after 12 months of regular unprotected intercourse, or 6 months for women over 35. Causes are varied, including hormonal disorders, structural problems, chronic illness, and male factor. Treatments include lifestyle changes and, when appropriate, assisted reproductive technologies such as in vitro fertilization, intrauterine insemination, and others. Population-level fertility can be influenced by access to contraception, education, and economic conditions, leading to wide regional differences in birth rates.