Determination of fetal heart rate reactivity from a single 20-min window of non-stress testing in compromised fetuses.

AIMS To shorten the analysis time needed for non-stress testing (NST) without decreasing efficacy in compromised fetuses. METHODS We selected 80 cases with a 5-min Apgar score <7 as a study group and 259 cases with a 5-min Apgar score >/=9 as a control group. We applied four different criteria (A, B, C, and D) to each study and control group for the first 20-min window of NST data to evaluate reactivity. Criteria A, B, and C consisted of conventional reactivity criteria according to amplitude (15 or 10 beats per minute), duration (15 or 10 s) and weeks of gestation (/=32), and criteria D combined criteria C with approximate entropy (ApEn). RESULTS The sensitivity of criteria D (91.25%) was greater than the other three criteria (P<0.0001). The specificities of criteria C (96.14%) and D (99.23%) were also higher than criteria A and B (P<0.0001). The positive and negative predictive value of criteria D were better than that of criteria C (97.33 vs. 83.87, P=0.0066) and (97.35 vs. 89.89, P=0.0004), respectively. CONCLUSION Adding ApEn to the conventional criteria for reactivity shortened NST analysis time without decreasing efficacy, facilitating a decision of reactivity within a single 20-min NST window.