Lactate as an early marker of intrapartum fetal hypoxia

Background: Cardiotocography (CTG) is the main method for intrapartum fetal surveillance in many countries. The method has a high sensitivity, but a poor specificity, which leads to an increased rate of interventions compared with auscultation. Fetal blood sampling (FBS) was developed parallel to CTG, and can be used as an adjunct to diagnose or exclude fetal acidemia when the CTG tracing is non-reassuring. Lactate analysis has been shown as reliable as gold standard pH analysis, and FBS with lactate analysis has the advantages of a lower failure rate, shorter time from sampling to analysis result, and lactate concentration identifies the metabolic component of acidemia in contrast to pH. However, since guidelines for CTG interpretation cannot be regarded as fully evidence-based, neither can guidelines for the use of FBS. The aim of this thesis was to further increase the knowledge of FBS and measurements of fetal lactate concentrations as an adjunct in intrapartum fetal surveillance. Materials and Methods: The study population consisted of women with a simplex pregnancy, gestational age ≥34 weeks, cephalic presentation and indication for FBS during labor. The cohort in papers I and II were women who had participated in a former RCT at ten obstetric units in Sweden. Study I included all 2992 women randomized to either pH-, or lactate analysis, and Study II included the 1496 women with lactate analysis. The cohort in studies III and IV were all consecutive women with FBS during labor at Karolinska University Hospital Solna, Sweden, during two years. In the 1st cohort, the 95th percentile of all lactate values and the 5th percentile of all pH values were used as the definition of severe intrapartum acidemia and frequencies of adverse neonatal outcome were calculated. The neonates were classified according to birth weight as small/appropriate/large, and medians in lactate concentration at FBS were calculated in the total population and in acidemic cases as well as neonatal outcome according to birth weight groups. ...