What is the normal range of maternal heart rate during the second stage of labor?

Normal Range of Maternal Heart Rate During the Second Stage of Labor

The normal range of maternal heart rate during the second stage of labor is typically 60-100 beats per minute (bpm) at baseline, but maternal tachycardia with heart rates ≥100 bpm occurs in approximately 33.9% of women, with 18.8% reaching ≥110 bpm and 9.1% reaching ≥120 bpm during pushing efforts.

Maternal Heart Rate Patterns During Second Stage Labor

Baseline Characteristics

• Normal maternal baseline heart rate between contractions: 80-90 bpm (average 88±14 bpm) 1
• During pushing efforts in second stage:
  • Average increase: +35±13 bpm from baseline 1
  • Average peak heart rate: 123±17 bpm during pushing 1
  • 27% of women maintain heart rates persistently >100 bpm throughout second stage 1
  • 20% of women reach peak heart rates >140 bpm during pushing efforts 1

Pattern Recognition

Maternal heart rate during second stage labor typically shows:

• Significant accelerations during pushing efforts
• Higher beat-to-beat variability compared to fetal heart rate 2
• More frequent accelerations and fewer decelerations compared to fetal heart rate 2

Clinical Implications

Potential for Monitoring Confusion

The high incidence of maternal tachycardia during second stage labor creates risk for confusing maternal and fetal heart rates:

• When maternal heart rate exceeds 100 bpm (occurs in 33.9% of women), there is increased risk of signal ambiguity 3
• Maternal heart rate patterns can mimic fetal heart rate patterns, including:
  • Accelerations during pushing efforts
  • Early-type decelerations between contractions 1, 2

Monitoring Recommendations

To avoid misinterpreting maternal heart rate as fetal heart rate:

1. Use simultaneous maternal and fetal heart rate monitoring when maternal heart rate ≥100 bpm 3
2. Be suspicious of tracings showing:
   • Repetitive accelerations during contractions with amplitude >20 bpm
   • Low baseline with early-type decelerations 1
3. Independently confirm fetal heart rate when patterns appear atypical

Factors Affecting Maternal Heart Rate During Second Stage

Interestingly, multivariate analysis of potential predisposing maternal conditions has not revealed any specific variable as uniformly significant for predicting maternal tachycardia during second stage labor 3.

Pitfalls to Avoid

1. Misinterpreting maternal heart rate as fetal heart rate - can lead to unnecessary interventions or missed fetal distress
2. Assuming tachycardia always indicates maternal pathology - tachycardia is common during pushing efforts
3. Failing to recognize the normal acceleration pattern - maternal heart rate typically increases significantly (+35 bpm on average) during pushing efforts 1
4. Not distinguishing between maternal and fetal patterns - maternal heart rate shows greater beat-to-beat variability and more pronounced accelerations during pushing 2

Understanding these normal maternal heart rate patterns during second stage labor is essential for accurate interpretation of monitoring data and appropriate clinical decision-making to optimize maternal and fetal outcomes.