Cervical dilation

Cervical dilation (or cervical dilatation) is the opening of the cervix, the entrance to the uterus, during childbirth, miscarriage, induced abortion, or gynecological surgery. Cervical dilation may occur naturally, or may be induced by surgical or medical means.

In the later stages of pregnancy, the cervix may already have opened up to 1–3 cm (or more in rarer circumstances), but during labor, repeated uterine contractions lead to further widening of the cervix to about 6 centimeters. From that point, pressure from the presenting part (head in vertex births or bottom in breech births), along with uterine contractions, will dilate the cervix to 10 centimeters, which is "complete." Cervical dilation is accompanied by effacement, the thinning of the cervix.

General guidelines for cervical dilation:

During pregnancy, the os (opening) of the cervix is blocked by a thick plug of mucus to prevent bacteria from entering the uterus. During dilation, this plug is loosened. It may come out as one piece, or as thick mucus discharge from the vagina. When this occurs, it is an indication that the cervix is beginning to dilate, although not all women will notice this mucus plug being released.

Bloody show is another indication that the cervix is dilating. Bloody show usually comes along with the mucus plug, and may continue throughout labor, making the mucus tinged pink, red or brown. Fresh, red blood is usually not associated with dilation, but rather serious complications such as placental abruption, or placenta previa. Red blood in small quantities often also follows an exam.

The pain experienced during dilation is similar to that of menstruation (although markedly more intense), as period pains are thought to be due to the passing of endometrium through the cervix. Most of the pain during labor is caused by the uterus contracting to dilate the cervix.

Prostaglandins (P2 and PGE2) contribute to cervical ripening and dilation. The body produces these hormones naturally. Sometimes prostaglandins in synthesized forms are applied directly to the cervix to induce labor. In women who have had a previous cesarean section, the American College of Obstetricians and Gynecologists issued a bulletin that misoprostol never be used for this purpose. ACOG's findings conclude that the collagen softening properties of misoprostol could be absorbed through the cervix and vaginal vault up into the low transverse scar of a typical cesarean section, and significantly increase the risk of uterine rupture. Prostaglandins are also present in human semen, and sexual intercourse is commonly recommended for promoting the onset of labor, although the limited data available makes the effectiveness of this method uncertain.

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