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I. Normal Labor
A. First Stage of Labor
1. The first stage of labor consists of the period from the onset of labor until complete cervical dilation (10 cm) pitocin, failure to progress, labor, oxytocin, cephalopelvic disproportion, distocia. This stage has been divided into the latent phase and the active phase.
2. Latent Phase
a. During the latent phase, uterine contractions are infrequent and irregular and result in only modest discomfort. They result in gradual effacement and dilation of the cervix.
b. A prolonged latent phase is one that exceeds 20 hours in the nullipara or one that exceeds 14 hours in the multipara.
3. Active Phase
a. The beginning of the active phase of labor occurs when the cervix reaches 3-4 cm of dilatation.
b. The active phase of labor is characterized by an increased rate of cervical dilation and by descent of the presenting fetal part.
B. Second Stage of Labor
1. The second stage of labor consists of the period from complete cervical dilation (10 cm) until delivery of the infant. This stage is usually brief, averaging 20 minutes for parous women and 50 minutes for nulliparous women.
2. The duration of the second stage of labor is unrelated to perinatal outcome in the absence of a nonreassuring fetal heart rate pattern as long as progress occurs.
II. Abnormal Labor
A. Dystocia is defined as difficult labor or childbirth resulting from abnormalities of the cervix and uterus, the fetus, the maternal pelvis, or combinations of these factors.
B. Cephalopelvic disproportion is a disparity between the size of the maternal pelvis and the fetal head that precludes vaginal delivery. This condition can rarely be diagnosed in advance. The term "failure to progress" should no longer be used.
C. Slower-than-normal (protraction disorders) or complete cessation of progress (arrest disorder). These disorders require the parturient to have entered the active phase of labor.
III. Assessment of Labor Abnormalities
A. Labor Abnormalities Due to Uterine Contractility. The minimal uterine contractile pattern of women in spontaneous labor consists of 3 to 5 contractions in a 10-minute period.
B. Labor Abnormalities Due to Fetal Characteristics
1. Assessment of the fetus consists of estimating fetal weight and position. Estimations of fetal size, even those obtained by ultrasonography, are frequently inaccurate.
2. In the first stage of labor, the diagnosis of dystocia can not be made unless the active phase of labor and adequate uterine contractile forces have occurred.
3. Fetal anomalies such as hydrocephaly, encephalocele, and softtissue tumors may obstruct labor. Fetal imaging should be consid ered when malpresentation or anomalies are suspected based on vaginal or abdominal examination or when the presenting fetal part is