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Am Fam Physician. 2021;103(2):90-96

This clinical content conforms to AAFP criteria for CME.

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Dystocia (abnormally slow or protracted labor) accounts for 25% to 55% of primary cesarean deliveries. The latent phase of labor begins with onset of regular, painful contractions and continues until 6 cm of cervical dilation. Current recommendations are to avoid admission to labor and delivery during the latent phase, assuming maternal/fetal status is reassuring. The active phase begins at 6 cm. An arrested active phase is defined as more than four hours without cervical change despite rupture of membranes and adequate contractions and more than six hours of no cervical change without adequate contractions. Managing a protracted active phase includes oxytocin augmentation with or without amniotomy. The second stage of labor begins at complete cervical dilation and continues to delivery. This stage is considered protracted if it lasts three hours or more in nulliparous patients without an epidural or four hours or more in nulliparous patients with an epidural. Primary interventions for a protracted second stage include use of oxytocin and manual rotation if the fetus is in the occiput posterior position. When contractions or pushing is inadequate, vacuum or forceps delivery may be needed. Effective measures for preventing dystocia and subsequent cesarean delivery include avoiding admission during latent labor, providing cervical ripening agents for induction in patients with an unfavorable cervix, encouraging the use of continuous labor support (e.g., a doula), walking or upright positioning in the first stage, and not diagnosing failed induction during the latent phase until oxytocin has been given for 12 to 18 hours after membrane rupture. Elective induction at 39 weeks' gestation in low-risk nulliparous patients may reduce the risk of cesarean delivery.

Labor dystocia refers to abnormally slow or protracted labor. It may be diagnosed in the first stage of labor (onset of contractions until complete cervical dilation) or the second stage of labor (complete cervical dilation until delivery). Dystocia is responsible for most cesarean deliveries. First- and second-stage arrest of labor may account for as many as 15% to 30% and 10% to 25%, respectively, of all primary cesarean deliveries.1 Table 1 defines protracted and arrested labor for each stage of labor.13

WHAT'S NEW ON THIS TOPIC

Labor Dystocia

A U.S. cohort study of 62,415 patients between 2002 and 2008 showed that the rate of cervical dilation in the active phase of labor was slower than that described by Friedman and that the transition point from latent to active labor was 6 cm rather than 4 cm.

A Cochrane review encompassing more than 15,000 patients reported that continuous labor support shortens labor by 35 minutes on average, reduces the risk of cesarean or operative vaginal delivery, and improves patients' satisfaction with their labor experience.

A 2017 meta-analysis of intravenous fluid administration showed that an infusion rate of 250 mL per hour in nulliparous patients may reduce the duration of labor and the cesarean delivery rate compared with 125 mL per hour.

Stage of laborProtracted laborArrested labor
First stage
 LatentNulliparous: > 20 hours
Multiparous: > 14 hours
Should not be diagnosed in the latent phase; prolonged latent labor alone is not an indication for cesarean delivery and does not require intervention
 ActiveDilation is nonlinear
Duration from 6 cm to full dilation is in the 95th percentile
 Nulliparous: 8.6 hours
 Multiparous: 7.5 hours
≥ 6-cm dilation, membrane rupture,
and either
> 4 hours without cervical change with adequate contractions*
or
> 6 hours without cervical change without adequate contractions
 Second stageWith epidural
 Nulliparous: ≥ 4 hours
 Multiparous: ≥ 3 hours
Without epidural
 Nulliparous: ≥ 3 hours
 Multiparous: ≥ 2 hours
Longer durations may be tolerated on a case-by-case basis when progress (rotation, descent) is documented and maternal/fetal status is reassuring; time in the second stage of labor is not an indication for cesarean or operative vaginal delivery

First Stage of Labor

The first stage of labor includes latent labor (beginning with the onset of regular, painful contractions) and active labor (beginning when the rate of cervical dilation accelerates).

DYSTOCIA DEFINITION

Traditionally, labor progress was defined as normal or abnormal based on data from the Friedman labor curve and was dependent on whether the patient was in latent or active labor.35 A more recent study of 62,415 pregnant people in U.S. hospitals between 2002 and 2008 showed that the rate of dilation in the active phase of labor was slower than that described by Friedman and that the transition point from latent to active labor was 6 cm rather than 4 cm.2 As a result, and in an effort to reduce cesarean deliveries performed because of slow labor progress before 6 cm of dilation, the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine revised their definitions and recommendations for the management of labor dystocia and arrest.3

MANAGEMENT

In the absence of other indications for delivery, prolonged latent labor in nulliparous patients generally does not require intervention as long as cervical dilation progresses. Specifically, it is not an indication for cesarean delivery because most patients with prolonged latent labor will eventually enter into active labor or will stop contracting.1,3

Arrest of labor should not be diagnosed before active labor begins (i.e., the cervix is dilated to 6 cm).13 Cesarean delivery should be reserved for patients meeting criteria for arrest of labor and who have undergone an adequate attempt at labor augmentation, including administration of oxytocin (Pitocin; titrated when possible until intrauterine pressure catheter shows contraction strength of at least 200 Montevideo units in 10 minutes) and amniotomy.68

In normally progressing, spontaneous labor, amniotomy alone does not shorten labor or reduce the cesarean delivery rate.9 When added to oxytocin in patients with a prolonged first stage, amniotomy shortens labor but does not reduce the cesarean delivery rate.10 When combined and used as a method of dystocia prevention, amniotomy and oxytocin are associated with only modest reductions in the cesarean delivery rate.10

Low-dose oxytocin regimens start at 0.5 to 2 mU per minute and increase by 1 to 2 mU per minute every 15 to 40 minutes. High-dose regimens start at 6 mU per minute and increase by 3 to 6 mU per minute every 15 to 40 minutes.11,12 Previous data suggested that high-dose regimens decreased the time to delivery11,13,14; however, a 2019 retrospective study of nulliparous patients did not show a faster time to delivery or reduction in the cesarean delivery rate when compared with low-dose regimens.15 A Cochrane review showed a decrease in uterine tachysystole (defined as more than five contractions in a 10-minute period, averaged over 30 minutes) with low-dose regimens compared with high-dose regimens, without a difference in the vaginal delivery rate within 24 hours or in the overall cesarean delivery rate.16 Given this evidence, physicians should use low-dose, rather than high-dose, oxytocin regimens when labor augmentation is required in nulliparous patients.

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