Infertility

Infertility
Specialty	Urology, gynecology
Causes	Common in females: annouvulation, blocked fallopian tube, hormonal imbalance Common in males: low sperm count, abnormal sperm morphology
Frequency	113 million (2015)[1]

Infertility is the inability of a couple to reproduce by natural means. It is usually not the natural state of a healthy adult. Exceptions include children who have not undergone puberty, which is the body's start of reproductive capacity. It is also a normal state in women after menopause.

In humans, infertility is the inability to become pregnant after at least one year of unprotected and regular sexual intercourse involving a male and female partner.^[2] There are many causes of infertility, including some that medical intervention can treat.^[3] Estimates from 1997 suggest that worldwide about five percent of all heterosexual couples have an unresolved problem with infertility. Many more couples, however, experience involuntary childlessness for at least one year with estimates ranging from 12% to 28%.^[4]

Male infertility is responsible for 20–30% of infertility cases, while 20–35% are due to female infertility, and 25–40% are due to combined problems in both partners.^[5] In 10–20% of cases, no cause is found.^[5] Male infertility is most commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.^[6] Male infertility may also be due to retrograde ejaculation, low testosterone, functional azoospermia (in which sperm is not produced or not produced in enough numbers) and obstructive azoospermia in which the pathway for the sperm (such as the vas deferens) is obstructed.^[2] The most common cause of female infertility is age, which generally manifests in sparse or absent menstrual periods leading up to menopause.^[7] As women age, the number of ovarian follicles and oocytes (eggs) decline, leading to a reduced ovarian reserve.^[2] Some women undergo primary ovarian insufficiency (also known as premature menopause) or the loss of ovarian function before age 40 leading to infertility.^[8] 85% of infertile couples have an identifiable cause and 15% is designated unexplained infertility.^[2] Of the 85% of identified infertility, 25% are due to disordered ovulation (of which 70% of the cases are due to polycystic ovarian syndrome).^[2] Tubal infertility, in which there is a structural problem with the fallopian tubes is responsible for 11-67% of infertility in women of child bearing age, with the large range in prevalence due to different populations studied.^[2] Endometriosis, the presence of endometrial tissue (which normally lines the uterus) outside of the uterus, accounts for 25-40% of female infertility.^[2]

Women who are fertile experience a period of fertility before and during ovulation, and are infertile for the rest of the menstrual cycle. Fertility awareness methods are used to discern when these changes occur by tracking changes in cervical mucus or basal body temperature.