Validity of short term variation (STV) in detection of fetal acidemia

Abstract

Aims: We aimed to establish a cut-off for short term variation (STV) in msec in electronic FHR tracings as a single parameter for the prediction of neonatal acidemia and hypercarbia at birth. Methods: 195 consecutive cases of singleton pregnancies between 26 to 42 weeks' gestation delivered by cesarean section, with an antepartum tracing performed within 4 hours from birth and umbilical artery gas analysis (UBGA) available at birth. Results: A positive correlation (r = 0.27, p < 0.0001) was found when STV was regressed against gestational age. We also found significant correlations between STV and UBGA parameters (pH [r = 0.12, p < 0.05] and pCO₂ [r =– 0.17, p < 0.01]). In order to evaluate the influence of gestational age on STV values, we subdivided patients into three subgroups (< 34 weeks: n = 31; 35-37 weeks: n = 37, and > 37 wks: n = 127). Only in the subgroup < 34 wks,STV < 5.1 msec was a significant predictor of acidemia (pH < 7.0), (sensitivity: 100%, specificity: 61%, p < 0.05); in the same subgroup STV < 4.9 msec predicted pCO2>60 mmHg with a sensitivity: 71.4% and a specificity: 62.5% (p < 0.02). Conclusion: In cases < 34 weeks' gestation, STV values below 4.9 msec and 5.1 msec are able to predict umbilical artery pH < 7.0 and PCO₂>60 mmHg, respectively.