Infertility Causes

Infertility is a common problem that affects 10-15% of couples. It is defined as the inability of a couple to conceive together after one year of regular, unprotected intercourse for women under age 35, or 6 months of regular, unprotected intercourse for women age 35 and above.

Infertility can be due to either or both partners.  Overall, a cause can be found in approximately 80% of cases and the remainder are unexplained.

Most common causes are:

  • Egg/Ovulatory dysfunction: 10–25%
  • Pelvic factor(s) (fallopian tube abnormalities, scarring, endometriosis etc.): 30–50%
  • Sperm/Male factor: 30–40%
  • Uterine/Cervical factor(s): 5–10%
  • Unexplained: 20–30%

The initial clinical assessment begins with a comprehensive history and exam of both partners. Laboratory and imaging tests are then performed to assess four key aspects for fertility in a couple: the sperm (male factor), the egg (ovarian reserve and ovulatory factor), transport (pelvic factor including fallopian tubes), and implantation of egg (uterus). It is also important to rule out any underlying thyroid or hormonal causes of infertility.

Female Causes of Infertility

Ovarian Reserve / Ovulatory Dysfunction

Ovarian reserve testing is an assessment of the reproductive potential of a woman. It is, essentially, a measure of the number and quality of the remaining egg follicle pool and is typically done with a simple pelvic ultrasound in addition to lab tests. The pelvic ultrasound is useful to measure the antral follicle count (visible follicles wherein each follicle houses an egg) and also allows for early identification of pelvic anatomical abnormalities. Labs tests such as follicle stimulating hormone (FSH) and estradiol hormone levels are also performed in the early part of the menstrual cycle. Anti-Müllerian hormone (AMH) is an additional marker of ovarian reserve that is gaining popularity. As ovarian reserve decreases, the ovaries’ responsiveness to medications given to stimulate egg follicle growth decreases, and this may indicate a need for higher amounts of FSH to achieve follicular growth and maturation during treatment. Studies also suggest that AMH levels may correlate with in vitro fertilization (IVF) success.

Ovulation is part of the menstrual cycle wherein a mature ovarian follicle expels its egg. Regular ovulation can often be assessed from a patient’s menstrual history. Basal body temperature charts, ovulation predictor kits, or elevated progesterone hormone levels can also be used to detect ovulation. Some women do not properly develop and release a mature egg every month and they therefore do not ovulate regularly. A lack of ovulation is called anovulation and infrequent or irregular ovulation is called oligoovulation. There are five main reasons why ovulation does not occur regularly include:

Polycystic ovarian syndrome (PCOS): syndrome characterized by two of the following: menstrual irregularities, androgen excess, and polycystic appearing ovaries on ultrasound. This condition affects 5-8% of reproductive age women.
Primary ovarian insufficiency (POI): condition when the number of eggs in the ovaries is very low and, as a result, the patient has irregular periods and symptoms of hot flashes. In order to meet criteria for this diagnosis the patient must be under 40 years of age.
Thryoid disease: either low or high thyroid levels can lead to irregular ovulation.
High prolactin levels: elevated prolactin (a milk producing hormone released by the brain) levels can also lead to irregular ovulation.
Hypothalamic dysfunction: can result if a patient is susceptible to certain stressors causing their brain to release subnormal amounts of the hormones necessary for ovulation.

Pelvic Factor(s)

Once the ovary releases the egg, the fallopian tube should pick up the egg. The egg then travels down the fallopian tube where it will encounter sperm and fertilization occurs. If there is a blockage (from prior pelvic infection, surgery, etc.), then the egg and sperm cannot meet. It is also possible to have scar tissue or endometriosis present in the abdomen/pelvis that can make the fallopian tubes unable to pick up the egg once it has been ovulated.

To test and ensure that the fallopian tubes are open, a hysterosalpingogram (HSG) is generally recommended. An HSG is an x-ray performed several days after the onset of menses. A dye is injected through the cervix into the uterine cavity and spills out the ends of patent fallopian tubes. It also allows for an assessment of the endometrial cavity.

Uterine / Cervical Factor(s)

When the injected dye during an HSG does not completely fill the uterine cavity, this is suggestive of a uterine irregularity and an intrauterine filling defect is diagnosed. These defects can be due to scar tissue, certain types of fibroids, and and/or polyps. A special saline ultrasound (where the uterus is filled with liquid) may be needed to further evaluate these irregularities.

An HSG can also show an overall abnormal uterine structure. Anomalies such as these are often congenital and can range from a septum that divides the uterine cavity, to more extreme malformations such as bicornuate uterus where the uterus has two horns. Congenital uterine anomalies are associated with pregnancy loss, but generally are not associated with infertility. However, uterine anomalies may be associated with severe endometriosis, which can impair fertility.

Cervical factors leading to infertility include structural causes (scarring, stenosis, in utero Diethylstilbestrol [DES] exposure), infection/cervicitis, and abnormal mucous production. It is important to ensure that a pap smear and an infectious evaluation are normal.


The diagnosis of unexplained infertility is assigned to couples with normal results of a standard infertility evaluation.

Sperm/Male Causes of Infertility

The presence of normal sperm is essential in achieving egg fertilization and subsequent pregnancy. Male infertility accounts for infertility in up to 30% of couples and testing is recommend early in the infertility evaluation. Sperm is tested by semen analysis wherein a sample is collected and analyzed. Male patients can have overall low sperm counts, a low percentage of sperm swimming, and/or a low percentage of sperm with normal shape.

There are four main causes of infertility in men: Men can have infertility due to disorders affecting parts of the brain called the hypothalamus and pituitary. In these men, certain hormones are not released normally in order to produce the normal amount of sperm. The second cause of male infertility is related to disease in the testicle. If there is any abnormality in the testes, this can lead to an abnormality with the sperm. A varicocele, for example, is a swelling of the veins around the testicular ducts (epididymis) and can cause a slowing of the blood flow with resultant increase in temperature around the testis. This interferes with sperm count and function and in certain cases may require surgical repair. The third cause is related to an obstruction in the transport of the sperm, and the fourth cause is deemed unexplained. Consultation with a reproductive urology specialist may be helpful in certain cases.