Factors Associated With Infertility

Although exact percentages vary somewhat with populations, approximately 85% to 90% of couples seeking infertility care are treated with medication or surgery, with 3% being treated with in vitro fertilization or other assisted reproductive methods (ASRM, 2016). About 40% of infertility is related to a male factor or a combined male and female factor (ASRM, 2016). About 20% of infertility is unexplained (Lobo, 2017). For those couples and individuals for whom a specific cause of infertility is not detected, the focus of infertility treatment has shifted from attempting to correct a specific pathology to recommending and initiating the treatment that is most effective in achieving pregnancy for this unique couple at this time in their reproductive life span. Assisted reproductive technologies (ARTs) have proven to be effective, even in couples who experience unexplained infertility.

Unassisted human conception requires a normally developed reproductive tract in both the male and female partners. For simplification, each live birth necessitates synchronization of the following:

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• The male must deposit semen with sperm that has the capacity to fertilize an egg close to the cervix at the time of ovulation. The sperm must be able to ascend through the uterus and uterine tubes (male factor). The cervix must be sufficiently open to allow semen to enter the uterus and provide a nurturing environment for sperm (cervical factor).

• The uterine tubes must be able to capture the ovum, transport semen to the ovum, and transport the fertilized embryo to the uterus (tubal factor).

• Ovulation of a healthy oocyte must occur, ideally within the parameters of a regular, predictable menstrual cycle (ovarian factor).

• The uterus must be receptive to implantation of the embryo and capable of nourishing the growth and development of the fetus throughout the normal duration of pregnancy (uterine factor).

An alteration in one or more of these structures, functions, or processes results in some degree of impaired fertility. Boxes 5.1 and 5.2 list factors affecting female and male infertility.