fecundability

Fecundability is the probability that a person or couple will conceive during a single menstrual cycle, given sexual intercourse without contraception and no known fertility problems. It is a measure of per-cycle reproductive efficiency and is distinct from fecundity, which refers to the biological capacity to conceive, and from infertility, which is the inability to conceive after a defined period of regular unprotected intercourse.

In epidemiology and reproductive medicine, fecundability is often estimated from time-to-pregnancy studies and reported as a per-cycle probability. Among healthy couples attempting conception, per-cycle fecundability is commonly cited in the range of about 20% to 25%, with substantial variation by age and health.

Fecundability declines with female age and can be influenced by male factors, ovulatory function, tubal patency, uterine health, and overall lifestyle. Factors such as body mass index, smoking, alcohol use, chronic illness, stress, and certain medications can reduce per-cycle probability. Irregular or anovulatory cycles reduce fecundability.

The concept is used in clinical counseling, population health research, and fertility treatment planning. It is related to but distinct from fecundity, time-to-pregnancy, and infertility definitions. Understanding fecundability helps characterize baseline fertility in populations and interpret how exposures or interventions may affect the likelihood of conception in any given cycle.