BACKGROUND: Fetal blood sampling for lactate estimation may be considered following identification of an abnormal or non-reassuring fetal heart rate pattern. The smaller volume of blood required for this test, compared with the more traditional pH estimation, may improve sampling rates. The appropriate use of this practice mandates systematic review of its safety and clinical effectiveness prior to widespread introduction. OBJECTIVES: To evaluate the effectiveness and risks of fetal scalp lactate sampling in the assessment of fetal well-being during labour, compared with no testing or alternative testing. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (November 2009). SELECTION CRITERIA: All published and unpublished randomised and quasi-randomised trials that compared fetal scalp lactate testing with no testing or alternative testing to evaluate fetal status in the presence of a non-reassuring cardiotocograph during labour. DATA COLLECTION AND ANALYSIS: Two review authors assessed the studies independently. MAIN RESULTS: The two identified randomised trials considered outcomes for 3348 mother-baby pairs allocated to either lactate or pH estimation of fetal blood samples in labour. There were no statistically significant differences for any fetal/neonatal/infant outcomes, including low Apgar score at five minutes, admission to neonatal intensive care units or neonatal encephalopathy, or for low umbilical arterial pH, base deficit or metabolic acidaemia. There was a statistically higher success rate for lactate compared with pH estimation (risk ratio 1.10, 95% confidence interval 1.08 to 1.12, n = 2992). There were no significant between-group differences in mode of birth or operative birth for non-reassuring fetal status. No studies reported outcomes of maternal satisfaction with fetal monitoring, anxiety, length of hospital stay or economic analysis. AUTHORS' CONCLUSIONS: When further testing to assess fetal well-being in labour is indicated, fetal scalp blood lactate estimation is more likely to be successfully undertaken than pH estimation. Action cut-off lactate values need to consider the lactate meter used. Further studies may consider sub-group analysis by gestational age, the stage of labour and sampling within a prolonged second stage of labour. Additionally, future studies may address longer-term neonatal outcomes, maternal satisfaction with intrapartum fetal monitoring and an economic analysis.