From the Guidelines
The onset of labor is best identified by the acceleration of cervical dilatation, which can be determined through serial vaginal examinations at least every 2 hours. This is based on the most recent and highest quality study available, which emphasizes the importance of monitoring cervical dilatation to accurately identify the beginning of the active phase of labor 1.
Key Signs of Labor Onset
- Accelerating cervical dilatation, which is the most reliable indicator of the onset of the active phase of labor
- Regular, painful contractions that increase in frequency and intensity, although these can be inconsistent and not always a reliable indicator of labor onset
- Rupture of membranes (water breaking), which may present as a sudden gush or a slow trickle of clear fluid
- Passing of the mucus plug, which may appear as a blood-tinged discharge
Assessing Labor Progression
Assessing uterine contractions, such as by palpation or using Montevideo Units, is of limited value in determining if a patient is in the active phase of labor, as contractions can be inconsistent and do not always increase in intensity, frequency, and duration over the course of the first stage of labor 1.
Clinical Decision Making
When assessing for the start of labor, it is essential to prioritize the acceleration of cervical dilatation as the primary indicator, as this is the most reliable sign of labor onset. Other signs, such as regular, painful contractions and rupture of membranes, can also be indicative of labor, but should be considered in conjunction with cervical dilatation findings. By prioritizing the acceleration of cervical dilatation, healthcare providers can make more accurate diagnoses and provide more effective care for patients in labor 1.
From the Research
Signs of Onset of Labor
The signs of onset of labor can be identified through various methods, including:
- Regular uterine contractions, which are a key indicator of labor 2
- Cervical dilation and effacement, which are signs of normal labor progress 3
- Changes in fetal heart rate patterns, such as accelerations and decelerations, which can be monitored using electronic fetal monitoring 4
- Uterine activity, including contraction frequency, duration, amplitude, and relaxation time, which can be monitored using various methods, including manual palpation, external tocodynamometry, and intrauterine pressure monitoring 2
Uterine Contractions
Uterine contractions are a crucial sign of labor, and their characteristics can be used to diagnose labor onset. These characteristics include:
- Frequency: regular contractions occurring at least once every 10 minutes 5
- Duration: contractions lasting for a certain period, typically 30 minutes or more 5
- Amplitude: the strength of the contractions, which can be measured using intrauterine pressure monitoring 2
- Relaxation time: the time between contractions, which can be used to assess uterine activity 2
Fetal Heart Rate Patterns
Fetal heart rate patterns can also be used to diagnose labor onset and assess fetal well-being. These patterns include:
- Normal baseline heart rate: between 110-160 beats per minute (bpm) 4
- Moderate variability: 6-25 bpm 4
- Accelerations: increases in fetal heart rate in response to uterine contractions 4
- Decelerations: decreases in fetal heart rate in response to uterine contractions, which can be classified as early, variable, late, or prolonged 4
Threatened Preterm Labor
Threatened preterm labor is a condition characterized by regular uterine contractions occurring before 37 weeks of gestation. The signs of threatened preterm labor include: