Obstetrics 5: Fetal Heart Tone Monitoring Portal
Indication: The goal of fetal heart tone (FHT) monitoring is to identify the fetus at risk for intrapartum demise or neurologic damage due to asphyxia and to institute appropriate management to improve the outcome. Abnormalities are most consistently identified by using continuous electronic fetal monitoring. Prior to 28 to 30 weeks, FHT acceleration may not be seen, as the fetus is too neurologically immature.
Reassuring
- Normal baseline rate (120 to 170) and variability (5 to 25 bpm). Irregularity of the baseline fetal heart rate (FHR) is one indication of the oxygenation status of the fetus.
- Lack of variable or late decelerations
- Presence of spontaneous acceleration
Warning
- Decreasing variability
- Increasing baseline rate. A significant fetal tachycardia is > 189 bpm. Consider the possibility of infection, anemia, prematurity, early hypoxia, betamimetic tocolytic effect, maternal tachycardia, and fever.
- Decreasing baseline rate: Causes to consider include fetal sleep, pregnancy-induced hypertension (PIH) where the mother is on magnesium sulfate. Analgesics, tranquilizers, narcotics, hypoxia, or extreme prematurity may be other causes of fetal sleep.
- Variable decelerations with normal beat-to-beat variability. Meconium-stained fluid
Ominous
- No baseline beat-to-beat variability
- Late decelerations
- Severe variable decelerations
- Bradycardia—90 to 100—is significant. Causes of significant bradycardia include hypoxia, conduction anesthesia, maternal hypothermia, and fetal heart conduction block. Mild bradycardia (FHR 100 to 120) may be caused by a post-dates fetus, occiput posterior presentation, or maternal medications, including narcotics and beta blockers.
Recognize and treat any significant variations in FHTs by changing maternal position, administering oxygen, performing amnioinfusion, or decreasing uterine activity by decreasing dose of Pitocin and/or administering terbutaline 0.25.
