Abnormal Labor and Induction of Labor

Key Points

Labor is a clinical diagnosis defined as uterine contractions that result in progressive cervical effacement and dilation.
The most common causes of protraction or arrest disorders are inadequate uterine activity and abnormal positioning of the fetal presenting part.
Under new guidelines, neither a protracted active phase nor arrest of dilation should be diagnosed in a nullipara before 6 cm cervical dilation.
Before a diagnosis of active-phase arrest is made, rupture of membranes should have occurred and the cervix must be dilated at least 6 cm, with either 4 hours or more of adequate contractions (e.g., more than 200 Montevideo units) or 6 hours or more of inadequate contractions and no cervical change.
Induction of labor should be undertaken when the benefits of delivery to either mother or fetus outweigh the risks of pregnancy continuation.
Studies have demonstrated that routine induction of labor at 41 weeks’ gestation is not associated with an increased risk of cesarean delivery regardless of parity, state of the cervix, or method of induction.
If elective induction is undertaken for nonmedical reasons, women should have pregnancies of 39 weeks’ gestation or more.
Induction of labor with IV oxytocin, intravaginal prostaglandin compounds, and expectant management (with defined time limits) are all reasonable options for women and their infants in the face of premature rupture of the membranes at term because they result in similar rates of neonatal infection and cesarean delivery.

Diagnosis

Abnormal Labor at Term

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The diagnosis of labor protraction and arrest should be considered based on the level of cervical dilation ( Table 13.1 ).

TABLE 13.1

Labor at Term (Zhang)

Data from Zhang J, Troendle J, Mikolajczyk R, et al. The natural history of the normal first stage of labor. Obstet Gynecol . 2010;115(4):705.
Data presented in hours as median (95th percentile).

Cervical Dilation (cm)	Parity 0	Parity 1	Parity 2+
From 3 to 4	1.2 (6.6)
From 4 to 5	0.9 (4.5)	0.7 (3.3)	0.7 (3.5)
From 5 to 6	0.6 (2.6)	0.4 (1.6)	0.4 (1.6)
From 6 to 7	0.5 (1.8)	0.4 (1.2)	0.3 (1.2)
From 7 to 8	0.4 (1.4)	0.3 (0.8)	0.3 (0.7)
From 8 to 9	0.4 (1.3)	0.3 (0.7)	0.2 (0.6)
From 9 to 10	0.4 (1.2)	0.2 (0.5)	0.2 (0.5)
From 4 to 10	3.7 (16.7)	2.4 (13.8)	2.2 (14.2)

Disorders of the Latent Phase

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Because the duration of latent labor is highly variable, even in the setting of a prolonged latent phase, expectant management is appropriate because most women will ultimately enter the active phase.

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