This unusual and uncommon FHR pattern has the appearance of a sine wave, with a cyclicity of three to five cycles per minute.
This pattern must persist for at least 20 minutes to qualify as a sinusoidal pattern.
With the classical sine wave pattern, there are no additional accelerations or decelerations. Variability is usually reduced, and sometimes absent.
![Sinusoidal Pattern 1 Sinusoidal Pattern](https://brooksidepress.org/mil_ob_gyn/wp-content/uploads/2015/06/efm_sinusoidal-e1434646221897-300x167.jpg)
The precise cause is unknown, but associations have been shown between this pattern and:
- Fetal anemia
- Fetal hypoxemia
- Maternal narcotic administration
If a sinusoidal pattern cannot be resolved with conventional measures, expedited delivery is usually undertaken.