Answer: <p><strong>Ovulation disorders</strong></p>
<p>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.</p>
<ul>
<li><strong>Polycystic ovary syndrome (PCOS).</strong> 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.</li>
<li><strong>Hypothalamic dysfunction.</strong> The two hormones responsible for stimulating ovulation each month &mdash; follicle-stimulating hormone (FSH) and luteinizing hormone (LH) &mdash; 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.</li>
<li><strong>Premature ovarian insufficiency.</strong> This disorder is usually caused by an autoimmune response where your body mistakenly attacks ovarian tissues or by the 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.</li>
<li><strong>Too much prolactin.</strong> 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.</li>
</ul>
<p><strong>Damage to fallopian tubes (tubal infertility)</strong></p>
<p>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:</p>
<ul>
<li>Pelvic inflammatory disease, an infection of the uterus and fallopian tubes due to chlamydia, gonorrhea or other sexually transmitted infections</li>
<li>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</li>
<li>Pelvic tuberculosis, a major cause of tubal infertility worldwide, although uncommon in the United States</li>
</ul>
<p><strong>Endometriosis</strong></p>
<p>Endometriosis occurs when tissue that normally grows in the uterus implants and grows in other locations. This extra tissue growth &mdash; and the surgical removal of it &mdash; 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.</p>
<p><strong>Uterine or cervical causes</strong></p>
<p>Several uterine or cervical causes can impact fertility by interfering with implantation or increasing the likelihood of a miscarriage.</p>
<ul>
<li>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.</li>
<li>Endometriosis scarring or inflammation within the uterus can disrupt implantation.</li>
<li>Uterine abnormalities present from birth, such as an abnormally shaped uterus, can cause problems becoming or remaining pregnant.</li>
<li>Cervical stenosis, a cervical narrowing, can be caused by an inherited malformation or damage to the cervix.</li>
<li>Sometimes the cervix can't produce the best type of mucus to allow the sperm to travel through the cervix into the uterus.</li>
</ul>
<p><strong>Unexplained infertility</strong></p>
<p>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.</p>