What are the signs of normal labor and how is labor progression monitored?

Signs of Normal Labor and Labor Progression Monitoring

The most reliable indicator of normal labor progression is cervical dilatation pattern, which should be monitored through serial vaginal examinations at least every 2 hours to accurately identify the onset of active labor and track its progression. 1

Normal Labor Phases and Signs

First Stage of Labor

• The first stage consists of two phases: latent and active 2
• The active phase begins when cervical dilation accelerates, regardless of the specific dilation measurement 2
• The American College of Obstetricians and Gynecologists and the World Health Organization recognize that active labor typically begins at 5-6 cm dilation, though this can vary 2, 3
• No diagnostic manifestations clearly demarcate active labor onset other than accelerating dilatation 1

Normal Cervical Dilatation Rates

• Normal dilatation rates in active phase are ≥1.2 cm/hour for nulliparas and ≥1.5 cm/hour for multiparas 2, 1
• The World Health Organization has rounded the nulliparous rate to 1.0 cm/hour for convenience in partogram use 1
• The rate of labor progression is highly variable among women but averages approximately 1.5 cm/hr 4

Uterine Contractions

• Regular uterine contractions increase in intensity, frequency, and duration during labor 5
• Contractions alone have limited value in determining if a patient is in active labor 1
• No abrupt change in contraction characteristics occurs to distinguish when active phase begins 1
• Later in labor, increased and more painful contractions often signal the beginning of the deceleration phase and fetal descent 1

Monitoring Labor Progression

Cervical Dilatation Monitoring

• Serial vaginal examinations (at least every 2 hours) are essential to detect when dilation rate increases from the flat slope of latent phase 1, 2
• Plotting cervical dilatation against time using a partogram is the most reliable method for identifying active labor onset and monitoring its progression 1
• The dilatation pattern is the only reliable indicator for prospectively identifying active labor onset 1

Fetal Descent Monitoring

• Monitoring fetal station is important alongside cervical dilatation 1
• Failure of descent is one of the abnormal labor patterns that can be detected 1

Uterine Activity Assessment

• Methods for evaluating uterine activity include:
  • Manual palpation
  • External tocodynamometry (most common)
  • Intrauterine pressure monitoring
  • Electrical uterine myometrial activity tracing 5
• Montevideo Units (sum of contraction amplitudes in mm Hg over 10 minutes) can be used to quantify contraction strength, with normal considered to be 200 units or more 1
• Objective tocodynamometry can identify labor onset earlier than subjective maternal perception 6

Recognizing Abnormal Labor Patterns

Active Phase Abnormalities

• Protracted dilatation: excessively slow rate of dilatation (<1.2 cm/h for nulliparas, <1.5 cm/h for multiparas) 1
• Arrest of dilatation: complete cessation of cervical dilatation 1
• Prolonged deceleration phase: extended slowing of dilatation near complete dilation 1
• Failure of descent: inadequate fetal descent despite continued cervical dilatation 1

Risk Factors for Labor Abnormalities

• Cephalopelvic disproportion
• Excessive neuraxial block
• Poor uterine contractility
• Fetal malpositions or malpresentations
• Uterine infection
• Maternal obesity
• Advanced maternal age
• Previous cesarean delivery 1, 2

Clinical Pitfalls and Caveats

• Establishing a fixed threshold (5-6 cm) for active labor onset may lead clinicians to ignore the possibility of active labor beginning at a lesser dilatation 3
• Ultrasound cervimetry studies have shown that labor patterns may differ from those originally described by Friedman, with some women not demonstrating clear deceleration phases 7
• Subjective maternal perception of contractions often lags behind objective measurements, with patients typically identifying labor onset hours after increased uterine activity is objectively recorded 6
• The rate of labor in nulliparous women can be highly variable and may not be affected by cervical dilation on admission 4