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Labor
Regular contractions of the uterus that cause dilation and thinning (effacement) of the cervix leading to the delivery of the infant.
 

Labor is divided into three stages . The  graph (Friedman curve) at right illustrates the traditionally expected rate of cervical dilation and duration of each stage of labor in a woman who has never given birth (nulliparous woman) [1].

The First Stage

The first stage of labor is characterized by dilatation of the cervix with descent of the fetal head into the pelvis. The first stage of labor is divided into a latent phase (early labor) and an active phase (active labor).


The latent phase (latent labor) begins when the mother feels regular uterine contractions accompanied by slow cervical dilation.

Zhang Labor Curve

In the past the active phase (active labor) has been defined as beginning when the cervix is dilated to 3 to 4 cm in the presence of uterine contractions. However, data from the Consortium on Safe Labor study suggests that in a present day population, 6 cm rather than 4 cm of cervical dilation may be a more appropriate landmark for the start of the active phase [2,3].

During the active phase uterine contractions become more frequent, the cervix dilates more quickly, and the baby descends into the pelvis. As the mother transitions from the end of the first stage of labor to the beginning of the second stage of labor her contractions may become more frequent and intense. During transition the mother may experience shaking, shivering, nausea, and vomiting. The active phase ends when the cervix has completely dilated to 10 centimeters.

First-stage arrest may be diagnosed if there is :

For spontaneous labor:
6 cm or greater dilation with membrane rupture AND 4 hours or more of adequate contractions (e.g., > 200 Montevideo units) OR
6 hours or more if contractions inadequate with no cervical change

For induced labor:
6 cm or greater dilation with membrane rupture or 5 cm or greater without membrane rupture AND 4 hours or more of adequate contractions (e.g., > 200 Montevideo units) OR
6 hours or more if contractions inadequate with no cervical change [4].

The Second Stage

The second stage of pregnancy begins when the cervix is fully dilated. The mother will usually feel a strong pressure in her rectum and an urge to push. As the infant's scalp becomes visible the mother will also feel burning and stinging. Loss of bowel or bladder control during the second stage is common. The second stage ends with delivery of the infant.

Second-stage arrest may be diagnosed if there has been
"No progress (descent or rotation) for
4 hours or more in nulliparous women with an epidural
3 hours or more in nulliparous women without an epidural
3 hours or more in multiparous women with epidural
2 hours or more in multiparous women without an epidural"[4]

The Third Stage

The third stage begins with delivery of the infant and ends with expulsion of the placenta. The third stage may last up to 30 minutes.


Reviewed by Mark Curran, M.D. FACOG
Updated 1/15/2014
REFERENCES:
1. Dystocia and augmentation of labor. ACOG Practice Bulletin No. 49. American College of Obstetricians and Gynecologists. Obstet Gynecol 2003;102:144554.
2. Zhang J, Landy HJ, Branch W, et al. Contemporary Patterns of Spontaneous Labor with Normal Neonatal Outcomes. Obstet Gynecol. 2010;116:12811287 PMID:21099592
3. Zhang J, et. al., Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol. 2002 Oct;187(4):824-8.PMID:12388957 4. Spong CY, et. al. Preventing the first cesarean delivery: summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, and American College of Obstetricians and Gynecologists Workshop. Obstet Gynecol. 2012 Nov;120(5):1181-93. doi http://10.1097/AOG.0b013e3182704880. PMID: 23090537

 
 

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