Fertility

Fertility is the biological capacity to produce offspring, culminating in live birth. In humans, fertility depends on the reproductive system of both male and female: the production of gametes and their viability, their union, implantation in the uterus, and continuation of pregnancy.

Fertility is distinguished from fecundity, which refers to the biological potential for reproduction, whereas fertility typically denotes births that have actually occurred. In population demography, fertility is measured by computed figures, such as the number of births per thousand people or the average number of children a woman bears in her lifetime.

Biological mechanism

In women, the menstrual cycle involves the release of an egg (ovulation), regulated by various hormones. The released egg remains viable for a short time only. In men, the testes continuously produce sperm; the count, motility, and morphology of sperm affect reproductive capacity. When an egg is fertilized, the embryo travels down the fallopian tube and implants in the uterus.

Age and health

Female fertility declines with age, especially after the mid-thirties, and ends at menopause. In men, the decline is slower but occurs. Other factors include body weight, smoking, alcohol consumption, sexually transmitted infections affecting the reproductive tract, and some cancer treatments.

Infertility and treatment

Infertility is typically investigated after one year of regular intercourse without conception. Investigation relies on sperm analysis, confirmation of ovulation, and imaging of the reproductive tract. Treatment ranges from medications stimulating ovulation to procedures such as in vitro fertilization (IVF). Causes are said to be roughly equally distributed between men and women, though some remain unexplained.

Population fertility

In population statistics, the measure used is the total fertility rate, the average number of children a woman would bear if she followed the age-specific fertility rates of a given year. Many countries have experienced declining fertility in recent centuries, linked to female education, family planning use, delayed marriage, and urbanization. Sub-Saharan African countries generally have higher rates than Europe and East Asia.