A sinusoidal fetal heart rate (FHR) pattern is characterized by repetitive, wave-like fluctuations with absent variability and no response to contractions; it is usually an ominous finding requiring immediate intervention (Option 4). A sinusoidal pattern (ie, a Category III FHR tracing) is suggestive of severe fetal anemia potentially due to fetomaternal hemorrhage (eg, abdominal trauma) or some fetal infections (eg, parvovirus B19).

If a sinusoidal pattern is noted, especially after abdominal trauma (eg, fall, motor vehicle collision, injury), the nurse should notify the health care provider immediately, initiate intrauterine resuscitation (eg, positioning, IV fluids, oxygen), and anticipate an expedited birth.

(Option 1) Fetal tachycardia (ie, FHR baseline >160 beats/min) may be caused by fetal anemia, maternal fever, or infection but is not more concerning than a sinusoidal pattern, particularly in this case because FHR accelerations and moderate variability are present.

(Option 2) Early decelerations mirror contractions with an apparent, gradual decrease in FHR (ie, ≥30 seconds from onset to nadir). Early decelerations indicate fetal head compression and are a normal finding.

(Option 3) Variable decelerations are abrupt decreases in the FHR (ie, <30 seconds from onset to nadir) and at least 15 beats/min below baseline for ≥15 seconds to <2 minutes. Variables are usually correctable with maternal position change to relieve umbilical cord compression. If recurrent/prolonged, variable decelerations can impair fetal oxygenation over time.

Educational objective:
A sinusoidal fetal heart rate pattern is usually an ominous finding associated with severe fetal anemia that requires intrauterine resuscitation and, potentially, an expedited birth.