INFERTILITY AND REPRODUCTIVE MEDICINE
CAUSES
Infertility can be caused by issues in the female reproductive system, the male reproductive system, or a combination of both. Each of these possibilities is about equally as likely the cause of fertility problems in couples who are not able to conceive. There are also cases in which - despite rigorous testing - a clear cause for the inability to achieve a pregnancy cannot be identified. In such cases, the cause for the infertility may be a genetic incompatibility of the partners, or other yet unknown reasons. The main causes for infertility in women are problems with either the ovaries (ovulation), Fallopian tubes (transport of the egg to the uterus and fertilization) or the uterus itself (implantation of the embryo and pregnancy). In men, the main cause for infertility are issues with the sperm (low sperm count, decreased sperm motility), the testes, or the vas deferens (the duct transporting the sperm to and though the penis). In some cases, prostate or other disorders of the reproductive organs can also be the cause of the infertility.
Female Infertility
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Ovarian disorders: The ovaries are the organs that produce and release an egg during each menstrual cycle (ovulation). Disorders in the ovaries, such as polycystic ovarian syndrome, can impair or inhibit ovulation, thereby leading to infertility. Because major reproductive hormones (such as the steroid hormones estrogen and progesterone) are produced in the ovaries, ovarian issues are often associated with hormonal imbalance, which can also contribute to infertility.
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Tubal disorders: The Fallopian tubes are the organs which transport the egg to the uterus. They are also where fertilization occurs if viable sperm is available. Infertility therefore can be the result of problems in the Fallopian tubes. For instance, if the tubes are blocked (such as because of inflammation, adhesions, or tumors) or if the cilia (thin hair-like structures in the tubes) don't work properly to propel the egg forward, the egg or embryo may not make it to the uterus to implant and initiate a pregnancy. Tubal blockages and adhesions causing infertility are often themselves the result of prior sexually transmitted diseases (infection leading to inflammation, also called salpingitis) or previous pelvic surgery.
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Uterine disorders: Infertility can also be caused by disorders in the uterus. For instance, if there are issues with the endometrium (uterine lining), such as endometriosis, the embryo may not be able to implant and grow properly, thereby preventing successful pregnancy. Similarly, if there are uterine fibroids (tumors), these might block the embryo's entry from the Fallopian tubes, or prevent the
embryo from growing properly due to lack of space or blood supply. -
Endocrine disorders: There are also hormonal (endocrine) disorders and imbalances that can cause infertility. For instance, hyperprolactinemia (an excess production of prolactin, a hormone released in the pituitary)
down regulates estrogen and therefore can be a factor contributing to infertility. Similarly, hyperthyroidism or hypothyroidism (an imbalance of thyroid hormones) can affect ovulation and thus decrease fertility. Abnormalities in other hormonal glads, specifically the hypothalamus (which releases the reproductive hormone GnRH) or the pituitary (which releases the reproductive hormone LH and FSH) may also lead to infertility. While such hormonal imbalances may be the result of specific endocrine disorders (or tumors in the endocrine glands), they can also be the consequence of normal aging, which leads to a reduction of reproductive hormones (especially estrogen) and thereby significantly reduces ovulation and fertility.
Male Infertility
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Testicular disorders: Sperm is produced in the testes. Therefore, testicular issues can lead to issues with sperm, such as low sperm count, decreased sperm motility, or dysfunctional sperm shape (morphology). For instance, blood vessel dysfunction such as varicoceles (blocked or enlarged testicular veins) can cause sperm abnormalities, because they raise the temperature in the testicles. Similarly, some chronic disorders, such as diabetes or obesity, as well as certain lifestyle choices, such as frequently using the hot tub, recreational drug use, alcohol consumption or smoking can have similar effects. STDs (such as HIV or chlamydia) can also result in severe and permanent sperm damage, and so can chemotherapy.
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Ductal disorders: The ducts (such as the epididymis or vas deferens) are the vessels that transport sperm from the testicles to the end of the penis. If there is a blockage in these ducts, sperm may not be able to exit the penis properly during ejaculation, in effect causing infertility. Ductal blockages can be the result of tumors, injuries (trauma), or infections (including STDs such as gonorrhea).
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Endocrine disorders: Hormonal imbalances can also affect sperm production and quality, and thereby fertility. For instance, decreased amounts of testosterone (produced and released in the testes) may reduce sperm count. Other hormonal issues, such as thyroid, pituitary or hypothalamic problems or tumors, can also similarly to infertility.