27.7A: Onset of Labor

Prodromal labor, which includes the latent phase of labor, marks the initial stages of parturition.

Learning Objectives

• Describe prodromal labor

Key Points

• Prodromal labor, the body’s preparation for real labor, may include an increase in blood volume, Braxton Hicks contractions, the presence of colostrum in the breasts, and the dislodging of the mucus plug.
• In contrast to Braxton Hicks contractions, the latent phase is marked by the point at which the woman perceives regular uterine contractions; cervical effacement will reach completion at the end of this stage.
• The latent phase ends with the onset of active first stage, which is marked by advanced dilation.
• The duration of labor varies widely, but its active phase averages some 20 hours for women giving birth to their first child (primiparae) and 8 hours for women who have already given birth (multiparae).
• In a caesarean section, the removal of the neonate is through a surgical incision in the abdomen, rather than through vaginal birth.

Key Terms

• caesarean section: A caesarean section, also known as C-section, is a surgical procedure in which one or more incisions are made through a mother’s abdomen (laparotomy) and uterus (hysterotomy) to deliver one or more babies, or, rarely, to remove a dead fetus.
• Braxton Hicks contractions: Known as false labor or practice contractions. They are sporadic uterine contractions that sometimes start around six weeks but are not usually felt until the second or third trimester of pregnancy.
• cervical effacement: The thinning and stretching of the cervix.
• parturition: The act or process of bearing or bringing forth offspring from the uterus; giving birth.

Pre-labor (First Stage of Labor)

Pre-labor, also called prodromal labor, consists of the early contractions and labor signs before actual labor starts. It is the body’s preparation for real labor.

Prodromal labor, often misnamed false labor, begins much as traditional labor but does not progress to the birth of the baby. Not everyone feels this stage of labor although it does always occur. However, this does not mean that every woman will experience every symptom.

The term is used to describe a cluster of physical changes that may take place in a pregnant woman before she goes into actual labor. These changes can include:

• An increase in blood volume (sometimes resulting in edema).
• Braxton Hicks contractions.
• The presence of colostrum in the breasts.
• The dislodging of the mucous plug that sealed the cervix during the pregnancy.

The term false labor is sometimes used to describe a cluster of Braxton Hicks contractions that are mistaken for real labor. The terms false labor and false pains are sometimes considered equivalent.

Latent Phase

The latent phase is generally defined as beginning at the point at which the woman perceives regular uterine contractions. In contrast, Braxton Hicks contractions should be infrequent, irregular, and involve only mild cramping.

Cervical effacement (the thinning and stretching of the cervix and cervical dilation) occurs during the closing weeks of pregnancy and is usually complete, or near complete, by the end of the latent phase.

When the contractions of labor begin, the walls of the uterus start to contract through stimulation by the release of the pituitary hormone oxytocin. The contractions cause the cervix to widen and begin to open.

As labor progresses the amniotic sac can rupture and cause a slow or a fast gush of fluids. Labor usually begins within a 24-hour period after the amniotic sac ruptures. As contractions become closer and stronger the cervix will gradually start to dilate.

The degree of cervical effacement may be felt during a vaginal examination. A long cervix implies that effacement has not yet occurred. At this stage, the cervix may dilate from 1 to 4 cm. The latent phase ends with the onset of the active phase, which is marked by an accelerated cervical dilation.