It is one of those questions where if we keep searching for reference, we get more and more confused whereas the answer lies is front of our eyes and we all know it. All of you know — contraction stress test “The contraction stress test (CST) is based on the response of FHR to uterine contractions, with the premise that fetal oxygenation will be worsened. This results in late decelerations in an already suboptimally oxygenated fetus. The test requires 3 contractions in 10 minutes, a positive or abnormal test is when late decelerations occur with more than half of the contractions, suspicious with any late decelerations, and negative with no late decelerations.” COGDT 10/e, p 255 So here is our answer, the most significant finding for hypoxia is late deceleration. Our answer is further supported by COGDT 10/e, p 257. “Late decelerations are smooth falls in the FHR begining after the contractions has started and ending after the contractions has ended. They are associated with fetal hypoxemia and potential for perinatal morbidity and mortality. Variable decelerations are abrupt in decline and return to baseline, vary in timing with the contractions, and usually represents cord compression.” As far as sinusoidal pattern is concerned - Williams Obs. 23/e, p 420 says “Intrapartum sinusoidal fetal heart patterns were not generally associated with fetal compromise”.