From the Guidelines
The criteria to assess for initiation of labor include monitoring for the transition from the latent phase to the active phase, characterized by an increase in the rate of cervical dilatation, which can be determined through serial vaginal examinations at least every 2 hours 1.
Key Assessment Criteria
- Cervical dilatation: The active phase of labor begins when the rate of dilatation increases, regardless of the degree of cervical dilatation achieved 1.
- Uterine contractions: While assessing uterine contractions can be done through palpation or Montevideo Units, it is of limited value in determining the active phase, as contractions inconsistently increase in intensity, frequency, and duration over the course of the first stage 1.
- Serial vaginal examinations: These are necessary to determine when the rate of dilatation increases, signaling the conversion to the active phase 1.
Important Considerations
- The active phase ends with a deceleration phase, which may be short and undetected, and can be followed by several aberrant labor patterns, including protracted dilatation, arrest of dilatation, and failure of descent 1.
- Underlying factors, such as cephalopelvic disproportion, excessive neuraxial block, poor uterine contractility, fetal malpositions, and maternal obesity, can contribute to active-phase disorders 1.
Clinical Decision-Making
- The most reliable method for prospectively identifying the onset of the active phase and assessing its progression is through serial graphing of cervical dilatation 1.
- When an active-phase disorder is identified, cesarean delivery may be justifiable if there is compelling clinical evidence of disproportion 1.
From the FDA Drug Label
Antepartum Oxytocin Injection, USP (synthetic) is indicated for the initiation or improvement of uterine contractions, where this is desirable and considered suitable, in order to achieve early vaginal delivery for fetal or maternal reasons It is indicated for (1) induction of labor in patients with a medical indication for the initiation of labor, such as Rh problems, maternal diabetes, pre-eclampsia at or near term, when delivery is in the best interest of mother and fetus or when membranes are prematurely ruptured and delivery is indicated;
The criteria to assess for initiation of labor include:
- Medical indications such as:
- Rh problems
- Maternal diabetes
- Pre-eclampsia at or near term
- Premature rupture of membranes
- Fetal or maternal reasons where early vaginal delivery is desirable and considered suitable 2
From the Research
Criteria for Assessing Initiation of Labor
The criteria for assessing initiation of labor include:
- Cervical dilatation and fetal station, which are used to create "labor curves" that provide diagnostic and prognostic information 3
- Cephalopelvic disproportion, excess analgesia, fetal malpositions, intrauterine infection, and maternal obesity, which are strongly associated with the development of labor disorders 3
- Clinical cephalopelvimetry, which involves assessing pelvic traits and predicting their effects on labor 3
- The use of exogenous oxytocin, which should be restricted to situations in which its potential benefits clearly outweigh its risks 3
Labor Progress Assessment
Labor progress can be assessed using:
- The labor curve, which describes the relationship between cervical dilation, station of the presenting part, and time 4
- Adaptive multifactorial models, which incorporate several factors related to labor progress and produce percentile rankings of dilation or station 5
- Continuous monitoring of cervical dilatation and fetal head station during labor, which can provide accurate and timely assessment of labor progression 6
Cervical Assessment
Cervical assessment is an important aspect of labor evaluation, and can be characterized by evaluating parameters such as: