This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis in Obstetrics, Subject name: Gynaecology & Obstetrics
True about significant variable decelerations is: 
Select and explain. 
A. Drop in fetal heart rate to less than 90 bpm for 60 seconds, B. Drop in fetal heart rate to less than 100 bpm for 60 seconds, C. Drop in fetal heart rate to less than 80 bpm for 60 seconds, D. Drop in fetal heart rate to less than 70 bpm for 60 seconds
D: Drop in fetal heart rate to less than 70 bpm for 60 seconds
Answer: D: Drop in fetal heart rate to less than 70 bpm for 60 seconds 
Explanation: Ans. is d, i.e. Drop in fetal heart rate to less than 70 bpm for 60 seconds Classification of variable decelerationDecelerationDefinitionMild variable deceleration>80 bpm irrespective of duration, or <30 seconds irrespective of depth or between FHR-70 to 80 bpm lasting for 60 secondsModerate variable deceleration>70 bpm lasting for 30 to 60 seconds or between FHR-70 to 80 bpm lasting for > 60 secondsSevere variable deceleration< 70 bpm lasting for 60 seconds