An abnormal labor may be referred to as dystocia, which simply means difficult labor or childbirth. In the active phase of the first stage or in the second stage of labor, an abnormal labor is identified when the rate of labor progress is slowed (protraction of labor) or stops altogether (arrest of labor). In order to determine if labor can be corrected to allow for vaginal delivery, the obstetrician must augment labor with oxytocin (Pitocin), a medication that stimulates the uterine contractions and is also used to induce labor. Definitions of abnormal labor are listed in Table 1.
Table 1. Definitions of Abnormal Labor
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Type of Abnormal Labor
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First-Time Pregnancy
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Subsequent Pregnancies
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| Protraction
|
|
|
| Dilatation (occurs in the active phase)
| Less than 1.2 centimeters of cervical dilatation per hour
| Less than 1.5 centimeters of cervical dilatation per hour
|
| Descent (primarily occurs in the second stage)
| Less than 1.0 centimeter of fetal head descent per hour
| Less than 2.0 centimeters of fetal head descent per hour
|
| Arrest
|
|
|
| Dilatation (occurs in the active phase)
| Same dilatation for more than 2 hours
| Same dilatation for more than 2 hours
|
| Descent (primarily occurs in the second stage)
| Same level of descent for more than 1 hour
| Same level of descent for more than 1 hour
|
A few examples of abnormal labor patterns may help you understand how the diagnosis of abnormal labor is made:
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Protraction of Dilation. The cervix dilates from 4 to 6 centimeters over 3 or 4 hours. This rate of dilation is slow, even in a first-time pregnancy. The expected dilatation over this period of time would be from 4 centimeters dilated to 7 to 8 centimeters dilated.
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Arrest of Dilation. The cervix is found to be 6 centimeters dilated on two examinations, one or two hours apart. Thus, no cervical dilation has occurred during the period of observation.
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Arrest of Descent. The head of the fetus is found to be at the same station in the birth canal on two different examinations, one hour apart. Arrest of descent is a diagnosis made in the second stage, after the cervix is completely dilated.
Uterine Hypocontractility
Labor may start out well, only later to stop or stall if the uterus fails to contract sufficiently. Sometimes this is caused by medications that lessen the intensity or frequency of the contractions. This type of abnormal labor is variously referred to as uterine inertia, uterine hypocontractility, or inadequate uterine power. Uterine hypocontractility is fairly common, especially in women having their first labor. In some centers that practice active management of labor, nearly 50% of all first pregnancies are treated with oxytocin to augment labor. However, uterine hypocontractility is less frequent in women who have previously been pregnant. These cases should be very carefully monitored before oxytocin is administered.
Cephalo-Pelvic Disproportion (CPD)
If the labor is still slow or stalled after oxytocin has been administered, the baby's head may simply be too large to fit through the birth canal. This condition is commonly called cephalo-pelvic disproportion (CPD). Vast experience has proven the only way to tell uterine hypocontractility from CPD is by trying to augment labor-uterine hypocontractility will be corrected and labor will progress normally, while labor will continue to stall in women with CPD. Women with CPD are delivered by cesarean section. With the proper use of oxytocin to augment labor, true CPD requiring cesarean section occurs in no more than 10 to 15% of women.
Go to Management of Labor.
For more information on labor, go to Inducing Labor and Pain Relief During Labor.
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