Fetal heart rate short term variation during labor in relation to scalp blood lactate concentration

Fetal heart rate short term variation ( STV ) decreases with severe chronic hypoxia in the antenatal period. However, only limited research has been done on STV during labor. We have tested a novel algorithm for a valid baseline estimation and calculated STV . To explore the value of STV during labor, we compared STV with fetal scalp blood ( FBS ) lactate concentration, an early marker in the hypoxic process. Material and methods Software was developed which estimates baseline frequency using a novel algorithm and thereby calculates STV according to Dawes and Redman in up to four 30‐minute blocks prior to each FBS . Cardiotocography traces from 1070 women in labor who had had FBS performed on 2134 occasions were analyzed. Results In acidemic cases (lactate >4.8 mmol/L; Lactate Pro™), median STV 30 minutes prior to FBS was 7.10 milliseconds compared with 6.09 milliseconds in the preacidemic (4.2‐4.8 mmol/L) and 5.23 milliseconds in the normal (<4.2 mmol/L) groups ( P  < .05). There was a positive correlation between lactate and STV (rho = 0.16‐0.24; P  < .05). Median lactate concentration in cases with STV <3.0 milliseconds (n = 160) was 2.3 mmol/L. When 2 FBS were performed within 60 minutes the change rate of lactate correlated to STV (rho = 0.33; P  < .001). Cases with increasing lactate concentration had a median STV of 5.29 milliseconds vs 4.41 milliseconds in those with decreasing lactate ( P  < .001). Conclusions In the early stages of intrapartum hypoxia, STV increases, contrary to findings regarding chronic hypoxia in the antenatal period. The increase in the adrenergic surge is a likely explanation.