From the Guidelines
Intrapartum begins with the onset of active labor, which is marked by an increase in the rate of cervical dilatation, regardless of the degree of dilatation achieved. This phase is characterized by regular uterine contractions that cause progressive cervical dilation, and it encompasses the entire labor process, including the first stage (cervical dilation), second stage (delivery of the baby), and third stage (delivery of the placenta) 1. The active phase of labor is identified by undertaking serial vaginal examinations at least every 2 hours to determine when the rate of dilatation increases from the negligible or absent slope of the latent phase to the more rapid progression of the active phase 1.
Key Points to Consider
- The onset of the active phase is signaled by an increase in the rate of cervical dilatation, not by a specific degree of dilatation 1.
- Assessing uterine contractions is of limited value in determining if a patient is in the active phase, as contractions inconsistently increase in intensity, frequency, and duration over the course of the first stage 1.
- The dilatation pattern is the most reliable indicator of the onset of the active phase and the normality of its progression, provided it is being graphed serially in labor 1.
- Healthcare providers confirm the start of intrapartum by documenting cervical changes through vaginal examinations, and the intrapartum period is physiologically marked by increased release of oxytocin and prostaglandins, which stimulate uterine contractions and facilitate the progressive dilation of the cervix to allow passage of the fetus through the birth canal.
Clinical Implications
- The active phase of labor begins at various degrees of dilatation when the rate of dilatation transitions from the relatively flat slope of the latent phase to a more rapid slope 1.
- Several aberrant labor patterns can be detected during the active phase, including protracted dilatation, arrest of dilatation, prolonged deceleration phase, and failure of descent, which may be associated with underlying factors such as cephalopelvic disproportion, excessive neuraxial block, poor uterine contractility, fetal malpositions, malpresentations, uterine infection, maternal obesity, advanced maternal age, and previous cesarean delivery 1.
From the Research
Definition of Intrapartum Period
The intrapartum period, also known as labor, is a complex process that involves various physiological changes.
- The onset of labor is typically marked by regular uterine contractions that lead to cervical dilatation and effacement 2.
- However, the exact timing of when the intrapartum period starts is not clearly defined in the provided studies.
Cervical Dilatation and Labor Progress
Cervical dilatation is an important indicator of labor progress, and various methods have been used to assess it, including digital vaginal examination (DVE) and intrapartum ultrasound 3, 4.
- Studies have shown that intrapartum ultrasound can provide accurate and reliable measurements of cervical dilatation, with good inter- and intra-observer agreement 4.
- The effects of individual uterine contractions on cervical dilatation and fetal head descent have also been evaluated, with findings suggesting that these effects vary during labor 5.
Onset of Labor
While the provided studies do not specifically define when the intrapartum period starts, they suggest that labor is a dynamic process that involves various physiological changes, including cervical dilatation and uterine contractions.
- The latent phase of labor, during which the cervix begins to dilate and efface, is an important part of the intrapartum period 2.
- However, the exact timing of when the intrapartum period starts is not clearly defined in the provided studies, and more research may be needed to determine the onset of labor.