Fetal Heart Rate Monitoring

 

Fetal Heart Rate (FHR) Monitoring

• Baseline FHR is measured over a 10-minute period.
• FHR is rounded to the nearest 5 bpm.
• Accelerations, decelerations, marked variability, and baseline segments differing by more than 25 bpm are not included in baseline calculations.

Normal Values

• Normal fetal baseline heart rate ranges from 110-160 bpm.
• Minimal variability is defined as fluctuations of less than 5 bpm.
• Moderate variability encompasses fluctuations of 6-25 bpm.
• Marked variability indicates fluctuations of more than 25 bpm.

Definition of Decelerations

• Acceleration: An abrupt increase of at least 15 bpm lasting more than 15 seconds but less than 2 minutes.
• Late deceleration: Gradual decrease in FHR returning to baseline, occurring after peak of contraction; onset to nadir takes 30 seconds or more.
• Early deceleration: Similar to late deceleration but occurs simultaneously with the peak of contraction.
• Variable deceleration: Abrupt drop in FHR, occurring in less than 30 seconds, decreasing 15 bpm or more below baseline, can happen with or without contractions.
• Prolonged deceleration: Drop below baseline of 15 bpm or more, lasting 2-10 minutes.

Classification of Decelerations

• Intermittent decels occur with less than 50% of contractions in a 20-minute segment.
• Recurrent decels occur with 50% or more of contractions in a 20-minute segment.

Uterine Activity Classifications

• Normal uterine activity consists of 5 or fewer contractions in a 10-minute segment, averaged over 30 minutes.
• Tachysystole is defined as more than 5 contractions in a 10-minute segment, averaged over 30 minutes.

Purpose and Frequency of EFM

• The primary purpose of Electronic Fetal Monitoring (EFM) is to assess if the fetus is well-oxygenated.
• EFM monitoring frequency:
  • No complications: every 30 minutes during the first stage, 15 minutes in the second stage.
  • With complications: every 15 minutes in the first stage, 5 minutes in the second stage.

Fetal Acid-Base Status Classification

• Classified using a 3-tiered system.

Predictors of Fetal Metabolic Acidemia

• Absence of fetal metabolic acidemia is indicated by moderate variability and the presence of accelerations.

Category Characteristics

• Category I: Baseline 110-160 bpm, moderate variability, absent late/variable decels, early decels present or absent.
• Category II: Minimal/absent/marked variability, absent accelerations, prolonged decels, recurrent late decels with moderate variability.
• Category III: Absent variability with recurrent late/variable decels or bradycardia, or sinusoidal pattern.

Interventions Based on FHR Patterns

• For minimal or absent variability or recurrent late decels: Administer 10 L oxygen on a nonrebreather mask to the mother.
• Technique for promoting fetal oxygenation: lateral positioning, IV fluid bolus, oxygen therapy, modification of pushing efforts, decrease/discontinue oxytocin.
• For tachysystole: reduce uterine activity through IV fluid bolus, lateral positioning, and may consider terbutaline if no improvement.
• For recurrent variable decelerations: alleviate umbilical cord compression via repositioning or amnioinfusion.
• For maternal hypotension: correct through lateral positioning, IV fluid bolus, or ephedrine if no response.
• Most medications (narcotics, cocaine, betamethasone, magnesium sulfate) typically lead to decrease in FHR variability.