Infertility is defined as the inability to conceive after at least one year of unprotected intercourse. According to this definition, statistics from 2002 indicate that 7.4% or 2.1 million married women aged 15-44 were infertile. The same statistics also showed that 12% or approximately 7.3 million married women aged 15-44 had “impaired fecundity” (a reduced ability to get pregnant or difficulty carrying a pregnancy to term). The incidence of infertility increases with age. In 2002, among all childless married women, 11% of those aged 15-29 were infertile, 17% of those aged 30-34 were infertile, 23% of those aged 35-39 were infertile, and 27% of those aged 40-44 were infertile.

Compared to past reports, the proportion of individuals with infertility and decreased fertility has not changed significantly since 1965. However, due to delayed childbirth and demographic changes, the number of older childless women has indeed increased. Additionally, the promotion of new infertility drugs and treatment technologies has spurred public interest and discussion about infertility. The number of people traveling to the US for IVF has also gradually increased.

Human fertility is relatively low. Assuming couples can conceive, the highest monthly pregnancy rate is 20% to 30%. Pregnancy failure is relatively common. A classic study by Hertig and Rock in 1949 reported that of 107 women who had intercourse and conceived in the ovulatory cycle before undergoing a hysterectomy, one-third of the early embryos studied were abnormal, based solely on morphological examination. 40% to 60% of pregnancies (with positive hCG values) fail around 12 weeks, with most fetal losses going unnoticed by the mother. Miscarriage rates appear to be related to maternal age: 7% to 15% for women under 30, 8% to 21% for women aged 30-34, 17% to 28% for women aged 35-39, and 34% to 52% for women over 40.