Nonstress test (NST)
Biophysical profile (BPP)
Vibroacoustic stimulation test (VSAT)
Contraction stress test/ oxytocin challenge
test (CST / OCT)
Fetal kick count
Color Doppler USG
Fetal heart rate (Doppler)
Fetal scalp electrode monitoring
Fetal pulse oximetry
Fetal scalp pH monitoring
Umbilical cord pH
- There is a decrease in baseline fetal heart rate of 24 beats/min between 16 weeks and term; or approximately 1 beat/min per week. This normal gradual slowing corresponds to maturation of parasympathetic (vagal) heart control.
- Bradycardia: The baseline fetal heart rate lesser than 110 beats/min.
- Tachycardia; The baseline fetal heart rate greater than 160 beats/min.
- Fetal hypoxia and hypercapnia can modulate the heart rate as it is also under the control of arterial chemoreceptors. More severe and prolonged hypoxia, with a rising blood lactate level and severe metabolic acidemia, induces a prolonged fall of heart rate due to direct effects on the myocardium.
- Some causes of fetal bradycardia include congenital heart block and serious fetal compromise (hypoxia/ acidosis).
- The most common explanation for fetal tachycardia is maternal fever.
- Other causes of fetal tachycardia include fetal compromise, cardiac arrhythmia, and maternal administration of atropine or terbutaline.
- Normal beat to beat variability should be 6-25 beats/minute.
- Diminished beat-to-beat variability can be an ominous sign and may indicate a seriously compromised fetus.
- Loss of beat-to-beat variability along with decelerations is associated with fetal acidemia.
- A common cause of diminished beat-to-beat variability is analgesic drugs given during labor.
- A large variety of CNS depressant drugs like narcotics, barbiturates, phenothiazines, tranquilizers, general anesthetics, and magnesium sulfate can cause transient diminished beat-to-beat variability.
Sinusoidal Heart Rate
- A true sinusoidal pattern is seen with serious fetal anemia, whether from D-isoimmunization, ruptured vasa previa, fetomaternal hemorrhage, parvo virus infection, or twin-to-twin transfusion. Insignificant sinusoidal patterns have been reported following administration of morphine.
- A sinusoidal pattern also has been described with chorioamnionitis, fetal distress (asphyxia), and umbilical cord occlusion.