Understanding Medical Aspects of Infertility: the Cervix and the Uterus

The uterus is a remarkable organ. It is composed primarily of muscle, known as myometrium. When not pregnant, it is about the size and shape of a small pear, but during pregnancy it can expand to hold a full-term infant. After delivery, it can then contract back down to essentially its original size.

The cervix is the part of the uterus that opens into the vagina; the main part of the uterus is known as the fundus. The cavity of the uterus, which when not pregnant is very small, is lined by a group of cells called the endometrium. It is these cells that undergo the regular monthly changes as a result of the hormones produced by the ovaries. These changes either allow implantation and a pregnancy to occur, or result in a menstrual period.

The first half of the menstrual cycle, the time from the start of the period until ovulation, is known as the proliferative phase because it is during this time that the lining of the uterus is thickening (proliferating). The part of the cycle between ovulation and the next period is known as the secretory phase; the lining is undergoing changes that will allow a pregnancy to implant should one occur. When a period occurs, this tissue is all shed (and secreted) and the whole cycle starts over again.

All of the anatomic problems of the uterus can be detected by either a physical exam, a hysterosalpingogram (an X-ray procedure), or by hysteroscopy (a surgical procedure in which a small instrument is inserted into the uterus and the uterine cavity visualized). If the hysterosalpingogram suggests that the uterine cavity is abnormal or the history and physical exam suggest such a problem may exist, hysteroscopy should be performed. Although diagnostic hysteroscopy can be performed in the office, any procedure done to correct an abnormality is probably best done in the operating room.

Under anesthesia, a small instrument that is connected to a light source is inserted through the cervix and into the uterus. The uterine cavity is distended using one of a number of different agents that affords the surgeon a better view of the inside of the uterus. Small surgical instruments can be introduced through the hysteroscope including scissors, lasers, and a variety of other instruments that allow the surgeon to correct many abnormalities. Polyps, fibroids, scarring of the uterine cavity, and some uterine anomalies can all be corrected this way.

Anomalies
When the uterus is formed, it begins as two tube like structures that begin on the side of the pelvis and come together in the middle. When they come together, the tissue in the middle is reabsorbed and the cavity is formed. In a small percentage of women, this process does not occur properly, and various anomalies can result. While few, if any, of these are associated with infertility, they may have other consequences such as recurrent pregnancy loss.

Fibroids
If a fibroid distorts the uterine cavity enough that it can be seen on X-ray or by hysteroscopy, it has probably compromised the blood supply to the endometrium that overlies it. If this blood supply is compromised, this tissue cannot function properly and undergo all of the changes that it should, and it may not be able to allow implantation.

Fibroids can also be pedunculated, or hanging into the uterine cavity from a stalk. The uterus does not like having anything in it with the exception of a fetus. Fibroids in the uterine cavity can result in much the same effect that occurs with an IUD—they irritate the uterus enough that it will not allow implantation to occur. Fibroids that distort the uterine cavity may be associated with bleeding at times other than the normal period. Consideration should be given to removing any fibroid within the uterine cavity or that distorts the uterine cavity.