Causes of infertility in women can basically be classified regarding whether they are acquired or genetic, or strictly by location.
Although female fertility factors can be classified as acquired versus genetic, it is mostly a combination of nature and nurture. The presence of any single risk factor of female infertility such as smoking, age or medication does not necessarily cause infertility, and even if a woman is definitely infertile then the infertility cannot definitely be blamed on any single risk factor.
Acquired: Age, Smoking, Sexually Transmitted Infections, and Being Overweight or Underweight can all affect fertility. Acquired factors practically include any factor that is not based on a genetic mutation, including any intrauterine exposure to toxins during fetal development, which may present as infertility many years later as an adult.
Age: A woman's fertility potential gradually declines after the age of 30. Higher rate of chromosomal abnormalities or health problems may be the reason for infertility in older women.
Tobacco smoking: Tobacco smoking by either of the partner reduces the couple’s chance of achieving a pregnancy and also reduces the possible benefit of fertility treatment. Smoking by the mother increases the chance of miscarriages.
Alcohol use: Alcohol increases the risk of birth defects and it may also make it harder to become pregnant.
Being overweight: Infertility can be due to sedentary lifestyle and due to overweight. A man's sperm count may also get affected if he is overweight.
Being underweight: Women at risk include those with eating disorders, such as anorexia nervosa or bulimia, and women following a very low calorie or restrictive diet.
Too much exercise: Exercising more than seven hours a week has been associated with ovulation problems. On the other hand, not enough exercise can contribute to obesity, which also increases infertility.
Environmental Factors: Exposure to environmental hazards such as herbicides, pesticides or industrial solvents may affect fertility. Phthalates, chemicals used to soften plastics, have the ability to disrupt hormones.
Stress and Fertility: Neurotransmitters act in the hypothalamus gland, which controls both reproductive and stress hormones. Severely elevated levels of stress hormone can, in fact, shut down menstruation.
Uterine or Abdominal Scarring: The scar tissue that forms following pelvic infection, appendicitis or pelvic surgery restricts the movement of ovaries and fallopian tubes and may cause infertility. Asherman syndrome that cause scarring in the uterus and cause obstructions and secondary amenorrhea. It may be caused by surgery, repeated injury, or unknown factors.
Diabetes mellitus: Despite modern treatment, women with diabetes are at increased risk of female infertility, such as reflected by delayed puberty and menarche, menstrual irregularities, mild hyperandrogenism, polycystic ovarian syndrome, fewer live born children and possibly earlier menopause.
Pelvic Inflammatory Disease: Pelvic inflammatory disease (PID) is a major cause of female infertility worldwide. PID comprises a variety of infections caused by different bacteria that affect the reproductive organs, appendix, and parts of the intestine that lie in the pelvic area. The sites of infection most often implicated in infertility are in the fallopian tubes, a specific condition referred to as salpingitis. Chlamydia, a sexually transmitted infection, is the most frequent cause of inflammation. Gonorrhea is responsible for most of the remaining cases. The inflammation of fallopian tube (salpingitis) results in blockage of the tube. Severe or frequent attacks of PID can eventually cause scarring, abscess formation, and tubal damage that result in infertility. PID also significantly increases the risk of ectopic pregnancy.
Endometriosis: It may account for as many as 30% of infertility cases and are involved directly or indirectly to infertility. The uterine tissue implants and grows outside of the uterus affecting the function of the sperm, egg and ovaries, uterus, and fallopian tubes. Endometriosis is a noncancerous condition and the uterine tissue that grow on other areas of the body, causes pain and irregular bleeding. Endometrial cysts may also cause infertility in several ways: they may block the egg's passage if the cyst is in fallopian tubes or prevent the release of egg if present in eggs. Severe endometriosis can eventually result in rigid webs of scar tissue between the uterus, ovaries, and fallopian tubes, thereby preventing the transfer of the egg to the tube.
Polycystic Ovarian Syndrome: Polycystic ovarian syndrome (PCOS) is a condition in which the ovaries produce high amounts of androgens or male hormones, especially testosterone which results in ovulation problems. PCOS occurs in about 6% of women, and amenorrhea or oligomenorrhea (infrequent menses) is quite common in PCOS. PCOS is also associated with insulin resistance and obesity. The elevated levels of androgens (hyperandrogenism) can cause obesity, facial hair, and acne, in some woman.
Ovulation disorders: These can be caused by faults in the regulation of reproductive hormones by the hypothalamus or the pituitary gland, or by problems in the ovary itself. The causes for ovulation disorders may be injury, tumors, excessive exercise and starvation or reaction to some medications. They prevent the ovaries from releasing eggs (anovulation). Ovulation disorders account for infertility in 25 percent of infertile couples.
Elevated prolactin levels (hyperprolactinemia): Prolactin is a hormone produced in the pituitary gland that stimulates breast development and milk production in association with pregnancy. High levels of prolactin in non pregnant woman may cause ovulation problems. High levels of prolactin (hyperprolactinemia) reduce gonadotropin hormones and inhibit ovulation. Some drugs, including oral contraceptives and some antipsychotic drugs, can also elevate levels of prolactin.
Thyroid problems: Disorders of the thyroid gland, either overactive thyroid gland (hyperthyroidism) or underactive thyroid gland (hypothyroidism) can interrupt the menstrual cycle and cause infertility.
Early menopause (Premature Ovarian Failure): The early depletion of ovarian follicles before age 40 result in early menopause. Certain conditions are associated with early menopause, including immune system diseases, radiation or chemotherapy treatment, and smoking, but still the cause is uncertain. It affects about 1% of women and is typically preceded by irregular periods, which might continue for years. In this condition, follicle-stimulating hormone (FSH) levels are elevated, as they are during perimenopause. Premature ovarian failure is a significant cause of infertility, and there is only 5 - 10% chance for the woman to conceive without fertility treatments. Adrenal, pituitary, or thyroid gland deficiencies, genetic disorders, such as Turner syndrome and fragile X syndrome or cancer treatments (radiation, chemotherapy, or both) can be responsible for early menopause condition.
Uterine fibroids: The benign tumors in the wall of the uterus may cause infertility by blocking the fallopian tubes. And most importantly, fibroids interfere with proper implantation of the fertilized egg.
Poor egg quality: Eggs that become damaged or with chromosomal abnormalities cannot sustain a pregnancy. It is an age related issue in which egg quality declines significantly in the late 30s and early 40s. 43 per cent of success is noted when a fertilised donor egg is implanted in women with poor egg quality.
Medications: Temporary infertility may occur with the use of certain medications. In most cases, fertility is restored when the medication is discontinued.
Cancer: Female reproductive cancers severely impair female fertility. Submucosal fibroids, ovarian cysts and tumors can obstruct the urinary tract. Both radiation and chemotherapy may affect a woman's ability to reproduce. Chemotherapy may impair reproductive function and fertility in men and women.
Other medical conditions: Medical conditions associated with delayed puberty or amenorrhea, such as Cushing's disease, sickle cell disease, kidney disease and diabetes, can affect a woman's fertility.
Sperm allergy: Fewer than 10 per cent of infertile women and men have immune reactions to sperm, which cause them to produce antibodies that kill sperm cells. In men, this is most common after a vasectomy. Sperm washing and intrauterine insemination, assisted conception treatments can help resolve this issue. Immunosuppressive drugs, such as cortisone and prednisone, are sometimes used but many doctors don't recommend them.
There are many gene mutations causes female infertility. Also, there are additional conditions involving female infertility which is believed to be genetic but where no single gene has been found to be responsible, notably Mayer-Rokitansky-Küstner-Hauser Syndrome (MRKH). An unknown number of genetic mutations cause a state of subfertility, which in addition to other factors such as environmental ones may manifest as frank infertility.
Congenital abnormalities: Abnormalities seen in genital tract by birth like Mullerian agenesis may cause infertility. Mullerian agenesis is a specific malformation in which no vagina or uterus develops. These women can undergo in vitro fertilization and with a surrogate mother they can continue the pregnancy.
Cervical narrowing or blockage: Also called cervical stenosis, can be caused by an inherited malformation or damage to the cervix. The cervix fails to produce the best type of mucus for sperm mobility and fertilization. In addition, the cervical opening may be closed, preventing any sperm from reaching the egg.
In some instances, a cause for infertility is never found. It's possible that combinations of minor factors in both partners underlie these unexplained fertility problems. The couples with unexplained infertility have the highest rates of spontaneous pregnancy of all infertile couples.