Variable deceleration features and intrapartum fetal acidemia - The role of deceleration area

In recent years deceleration area has received increasing attention as a potential predictor of intrapartum fetal hypoxia. In several studies, the area has been manually esteemed as triangular in shape, which might introduce bias. In addition, the commonly used outcome acidemia in umbilical artery is affected by mode of delivery. We wanted to investigate the association between the variable deceleration features area, duration, depth and cumulative deceleration area (30 and 60 min) and intrapartum fetal acidemia measured as lactate concentration at fetal scalp blood sampling (FBS) in immediate connection to the decelerations.

In the source population of 1070 labors at Karolinska University Hospital, Sweden, with FBS performed on indication, we found 507 fetuses with predominantly variable decelerations as the indication for FBS. We examined the last 60- and 30-minutes of fetal monitoring preceding the FBS with focus on deceleration area, duration and depth. The contours of the decelerations were outlined manually but the area was calculated with a computer software program. We assessed area, duration and depth both as mean values per deceleration and as cumulative values during the time period of interest. We analyzed Pearson correlations and area under receiver operating characteristics curves (AUC). We also performed an adjusted analysis, with baseline frequency, variability, and accelerations as covariates.

Deceleration area and duration were the best predictors of intrapartum fetal acidemia (fetal lactate concentration >4.8 mmol/L measured with Lactate Pro™) with AUCs of 0.671 (0.682) and 0.678 (0.683) for cumulative measures during 30 (60) minutes prior to FBS, compared to deceleration depth with AUC of 0.632 (0.631). Corresponding Pearson correlations in 30-min (60-min) groups were 0.329 (0.335) and 0.358 (0.354) for deceleration area and duration and 0.212 (0.204) for deceleration depth. Using 250 beats cumulative cut-off for deceleration area during last 30 min, 71% vs. 43% were acidemic and non-acidemic, odds ratio = 3.2 (95% CI 1.7-6.1).

Deceleration area and duration were better predictors of intrapartum fetal acidemia than deceleration depth. Cumulative deceleration area >250 beats during 30 min was associated with three-fold higher odds of intrapartum acidemia compared to <250 beats.