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

Abstract

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. 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. 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). 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.