<|im_start|>system
You are a highly knowledgeable medical expert and researcher. Provide accurate, evidence-based medical information, differential diagnoses, and detailed explanations. Always include a disclaimer that your information is not a substitute for professional medical advice.<|im_end|>
<|im_start|>user
Question: Sinusoidal heart rate pattern is seen in:
Options:
A. Placenta previa
B. Vasa previa
C. Battledore placenta
D. Succenturiate placenta
Which is the correct option?<|im_end|>
<|im_start|>assistant
The correct option is B: Vasa previa. Explanation: Sinusoidal Pattern:

Stable baseline heart rate of 120 to 160 beats/min with regular oscillations.
Amplitude of 5 to 15 beats/min (rarely greater).
Long-term variability frequency of 2 to 5 cycles per minute.
Fixed or flat short-term variability.
Oscillation of the sinusoidal waveform above or below a baseline.
Absence of accelerations.

Causes of Sinusoidal Pattern:

Serious fetal anemia due to Rh-isoimmunisation/rupture vasa previa / feto maternal hemorrhage / twin to twin transfusion.
Drugs — Meperidine, morphine, alpha prodine and butorphanol.
Amnionitis.
Fetal distress (+/–).
Umbilical cord occlusion.<|im_end|>
