CausesBy Mayo Clinic staff
To become pregnant, each of these factors is essential:
- You need to ovulate. Achieving pregnancy requires that your ovaries produce and release an egg, a process known as ovulation. Your doctor can help evaluate your menstrual cycles and confirm ovulation.
- Your partner needs sperm. For most couples, this isn't a problem unless your partner has a history of illness or surgery. Your doctor can run some simple tests to evaluate the health of your partner's sperm.
- You need to have regular intercourse. You need to have regular sexual intercourse during your fertile time. Your doctor can help you better understand when you're most fertile during your cycle.
- You need to have open fallopian tubes and a normal uterus. The egg and sperm meet in the fallopian tubes, and the pregnancy needs a healthy place to grow.
For pregnancy to occur, every part of the complex human reproduction process has to take place just right. The steps in this process are as follows:
- One of the two ovaries releases a mature egg.
- The egg is picked up by the fallopian tube.
- Sperm swim up the cervix, through the uterus and into the fallopian tube to reach the egg for fertilization.
- The fertilized egg travels down the fallopian tube to the uterus.
- The fertilized egg implants and grows in the uterus.
In women, a number of factors can disrupt this process at any step. Female infertility is caused by one or more of these factors.
Ovulation disorders, meaning you ovulate infrequently or not at all, account for infertility in about 25 percent of infertile couples. These can be caused by flaws in the regulation of reproductive hormones by the hypothalamus or the pituitary gland, or by problems in the ovary itself.
- Polycystic ovary syndrome (PCOS). In PCOS, complex changes occur in the hypothalamus, pituitary gland and ovaries, resulting in a hormone imbalance, which affects ovulation. PCOS is associated with insulin resistance and obesity, abnormal hair growth on the face or body, and acne. It's the most common cause of female infertility.
- Hypothalamic dysfunction. The two hormones responsible for stimulating ovulation each month — follicle-stimulating hormone (FSH) and luteinizing hormone (LH) — are produced by the pituitary gland in a specific pattern during the menstrual cycle. Excess physical or emotional stress, a very high or very low body weight, or a recent substantial weight gain or loss can disrupt this pattern and affect ovulation. The main sign of this problem is irregular or absent periods.
- Premature ovarian insufficiency. This disorder is usually caused by an autoimmune response where your body mistakenly attacks ovarian tissues or by premature loss of eggs from your ovary due to genetic problems or environmental insults such as chemotherapy. It results in the loss of the ability to produce eggs by the ovary, as well as a decreased estrogen production under the age of 40.
- Too much prolactin. Less commonly, the pituitary gland can cause excess production of prolactin (hyperprolactinemia), which reduces estrogen production and may cause infertility. Most commonly this is due to a problem in the pituitary gland, but it can also be related to medications you're taking for another disease.
Damage to fallopian tubes (tubal infertility)
When fallopian tubes become damaged or blocked, they keep sperm from getting to the egg or block the passage of the fertilized egg into the uterus. Causes of fallopian tube damage or blockage can include:
- Pelvic inflammatory disease, an infection of the uterus and fallopian tubes due to chlamydia, gonorrhea or other sexually transmitted infections
- Previous surgery in the abdomen or pelvis, including surgery for ectopic pregnancy, in which a fertilized egg becomes implanted and starts to develop in a fallopian tube instead of the uterus
- Pelvic tuberculosis, a major cause of tubal infertility worldwide, although uncommon in the United States
Endometriosis occurs when tissue that normally grows in the uterus implants and grows in other locations. This extra tissue growth — and the surgical removal of it — can cause scarring, which may obstruct the tube and keep the egg and sperm from uniting. It can also affect the lining of the uterus, disrupting implantation of the fertilized egg. The condition also seems to affect fertility in less-direct ways, such as damage to the sperm or egg.
Uterine or cervical causes
Several uterine or cervical causes can impact fertility by interfering with implantation or increasing the likelihood of a miscarriage.
- Benign polyps or tumors (fibroids or myomas) are common in the uterus, and some types can impair fertility by blocking the fallopian tubes or by disrupting implantation. However, many women who have fibroids or polyps can become pregnant.
- Endometriosis scarring or inflammation within the uterus can disrupt implantation.
- Uterine abnormalities present from birth, such as an abnormally shaped uterus, can cause problems becoming or remaining pregnant.
- Cervical stenosis, a cervical narrowing, can be caused by an inherited malformation or damage to the cervix.
- Sometimes the cervix can't produce the best type of mucus to allow the sperm to travel through the cervix into the uterus.
In some instances, a cause for infertility is never found. It's possible that a combination of several minor factors in both partners underlie these unexplained fertility problems. Although it's frustrating to not get a specific answer, this problem may correct itself with time.
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