What is a common clinical feature of fetal heart rate patterns associated with sinusoidal FHR?

Sinusoidal fetal heart rate patterns are characterized by smooth, regular oscillations in the fetal heart rate typically occurring in a waveform that resembles a sine wave. This pattern indicates a unique rhythm and is often associated with concerning fetal conditions, such as severe fetal anemia or fetal hypoxia.

The defining feature of this pattern is its consistent and periodic oscillations, which can be visually identified on a fetal heart rate strip as a series of oscillations around a baseline heart rate, with a frequency of about 5–10 cycles per minute. Unlike other types of decelerations, which may show variable changes in heart rate in response to fetal movements or uterine contractions, the regular oscillations of the sinusoidal pattern signify a more stable, yet pathological, rhythm that reflects the heart rate’s predictable fluctuations.

In comparison, late decelerations are characterized by a gradual decrease in the heart rate in response to uterine contractions and are indicative of possible placental insufficiency. Variable decelerations show abrupt decreases in heart rate due to umbilical cord compression and vary in timing and shape. Sustained normal baseline implies a stable heart rate without the oscillations present in a sinusoidal pattern. Therefore, the defining characteristic of the sinusoidal fetal heart rate pattern