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] The most common cause of female infertility is age, which generally manifests in sparse or absent menstrual periods leading up to menopause.

Fertility awareness methods are used to discern when these changes occur by tracking changes in cervical mucus or basal body temperature.

[9] Currently, female fertility normally peaks in young adulthood and diminishes after 35 with pregnancy occurring rarely after age 50.

Existing definitions of infertility lack uniformity, rendering comparisons in prevalence between countries or over time problematic.

[13] Updated NICE guidelines do not include a specific definition, but recommend that "A woman of reproductive age who has not conceived after 1 year of unprotected vaginal sexual intercourse, in the absence of any known cause of infertility, should be offered further clinical assessment and investigation along with her partner, with earlier referral to a specialist if the woman is over 36 years of age.

[15] Primary infertility is defined as the absence of a live birth for women who desire a child and have been in a union for at least 12 months, during which they have not used any contraceptives.

Advances in assisted reproductive technologies, such as IVF, can offer hope to many couples where treatment is available, although barriers exist in terms of medical coverage and affordability.

The medicalization of infertility has unwittingly led to a disregard for the emotional responses that couples experience, which include distress, loss of control, stigmatization, and a disruption in the developmental trajectory of adulthood.

It is also possible that women feel a sense of hopefulness/increased optimism prior to initiating infertility treatment, which is when most assessments of distress are collected.

Researchers have also shown that despite a good prognosis and having the finances available to pay for treatment, discontinuation is most often due to psychological reasons.

The stress of the non-fulfilment of a wish for a child has been associated with emotional consequences such as anger, depression, anxiety, marital problems and feelings of worthlessness.

[5] The most common cause of female infertility are ovulation problems, usually manifested by scanty or absent menstrual periods.

[30] Before puberty, humans are naturally infertile; their gonads have not yet developed the gametes required to reproduce: boys' testicles have not developed the sperm cells required to impregnate a female; girls have not begun the process of ovulation which activates the fertility of their egg cells (ovulation is confirmed by the first menstrual cycle, known as menarche, which signals the biological possibility of pregnancy).

The absence of fertility in children is considered a natural part of human growth and child development, as the hypothalamus in their brain is still underdeveloped and cannot release the hormones required to activate the gonads' gametes.

[35] In both men and women, ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome reaction, impaired fertilization, influence on the implantation process, and impaired growth and development of the embryo.

Factors contributing to the formation of antisperm antibodies in women are disturbance of normal immunoregulatory mechanisms, infection, violation of the integrity of the mucous membranes, rape and unprotected oral or anal sex.

Risk factors for the formation of antisperm antibodies in men include the breakdown of the blood‑testis barrier, trauma and surgery, orchitis, varicocele, infections, prostatitis, testicular cancer, failure of immunosuppression and unprotected receptive anal or oral sex with men.

[35][36] Infections with the following sexually transmitted pathogens have a negative effect on fertility: Chlamydia trachomatis and Neisseria gonorrhoeae.

Infertility may be caused by blockage of the fallopian tube due to malformations, infections such as chlamydia or scar tissue.

World Health Organization subdivided ovulatory disorders into four classes: Malformation of the eggs themselves may complicate conception.

For example, polycystic ovarian syndrome (PCOS) is when the eggs only partially develop within the ovary and there is an excess of male hormones.

In this case, synthetic FSH by injection or Clomid (Clomiphene citrate) via a pill can be given to stimulate follicles to mature in the ovaries.

In men who have the necessary reproductive organs to procreate, infertility can be caused by low sperm count due to endocrine problems, drugs, radiation, or infection.

[2] Adeno-associated virus infection has been linked to poor sperm quality and may contribute to male infertility, based on small observational studies.

[77][78] If both partners are young and healthy and have been trying to conceive for one year without success, a visit to a physician or women's health nurse practitioner (WHNP) could help to highlight potential medical problems earlier rather than later.

[79] However, there are instances where couples should seek reproductive counseling after only 6 months of trying for a pregnancy: A doctor or WHNP takes a medical history and gives a physical examination.

According to ESHRE recommendations, couples with an estimated live birth rate of 40% or higher per year are encouraged to continue aiming for a spontaneous pregnancy.

[2] In some cases, in vitro fertilization (IVF) is used in which induced ovarian follicle stimulation is followed by extraction of oocytes from the ovaries.

[84] Ovarian stimulation (such as with clomiphene) combined with in-vitro fertilization or intra-uterine insemination have lower success rates with increasing age.