Fetal blood sampling and scalp lactate

You are 40 minutes into an abnormal trace. The oxytocin is off, she is on her side, the fluid is running, the cord is not prolapsed — and the decelerations are still there with reduced variability. The registrar's instinct is to sample. The consultant's question is different: what will you do differently at 7.24 that you would not do at 7.26? If you cannot answer that, the needle is a delay dressed as a decision.^[7][10]

This is also a mandatory RANZCOG Basic Obstetric Skills workshop station, so the procedural detail — position, prerequisites, kit, technique, thresholds — is guaranteed examinable.^[17]

Overview — what the test measures and what it does not

A fetal blood sample is a few microlitres of capillary blood from the presenting part, analysed for acid-base status at one instant in labour.^[14][1]

• It measures acidaemia, not oxygenation. It tells you what has already accumulated, not what is happening now.^[14]
• It is a single time point. Labour is a process; the sample is a photograph. That is why the repeat interval matters more than the first number.^[17][14]
• It exists to reduce unnecessary operative birth. Continuous CTG increases caesarean and instrumental birth; fetal blood sampling was introduced as the tie-breaker that would give some of that back.^[18][7]

^{[17] [1] [2]}

References20ShowHide

1. [1]Wiberg-Itzel E, Lipponer C, Norman M, et al. Determination of pH or lactate in fetal scalp blood in management of intrapartum fetal distress: randomised controlled multicentre trial BMJ, 2008.PMID 18503103
2. [2]East CE, Leader LR, Sheehan P, et al. Intrapartum fetal scalp lactate sampling for fetal assessment in the presence of a non-reassuring fetal heart rate trace Cochrane Database Syst Rev, 2015.PMID 25929461
3. [3]Iorizzo L, Carlsson Y, Johansson C, et al. Proposed cutoff for fetal scalp blood lactate in intrapartum fetal surveillance based on neonatal outcomes: a large prospective observational study BJOG, 2022.PMID 34555249
4. [4]Westgren M, Kruger K, Ek S, et al. Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study Br J Obstet Gynaecol, 1998.PMID 9442158
5. [5]Kruger K, Hallberg B, Blennow M, et al. Predictive value of fetal scalp blood lactate concentration and pH as markers of neurologic disability Am J Obstet Gynecol, 1999.PMID 10561620
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7. [7]Garabedian C, Girault A Should fetal blood sampling still be a part of monitoring during labor in the modern era ? J Gynecol Obstet Hum Reprod, 2025.PMID 40581336
8. [8]Gröndal K, Gyllencreutz E, Wretler S, et al. Frequency of fetal blood sampling, delivery mode and neonatal outcome after revised CTG-classification and updated lactate meter in Sweden: An observational study Acta Obstet Gynecol Scand, 2025.PMID 39917811
9. [9]West S, Ibiebele I, Nippita T Intrapartum fetal blood sampling performed at early cervical dilatation and delivery outcomes Aust N Z J Obstet Gynaecol, 2021.PMID 33382081
10. [10]Lowe B, Beckmann M Involving the consultant before fetal blood sampling Aust N Z J Obstet Gynaecol, 2016.PMID 27297955
11. [11]Tahir Mahmood U, O'Gorman C, Marchocki Z, et al. Fetal scalp stimulation (FSS) versus fetal blood sampling (FBS) for women with abnormal fetal heart rate monitoring in labor: a prospective cohort study J Matern Fetal Neonatal Med, 2018.PMID 28475393
12. [12]Murphy DJ, Shahabuddin Y, Yambasu S, et al. Digital fetal scalp stimulation (dFSS) versus fetal blood sampling (FBS) to assess fetal wellbeing in labour-a multi-centre randomised controlled trial: Fetal Intrapartum Randomised Scalp Stimulation Trial (FIRSST NCT05306756) Trials, 2022.PMID 36195894
13. [13]Liljeström L, Wikström AK, Hanson U, et al. Evaluation of the discrepancy between pH and lactate in combined fetal scalp blood sampling Acta Obstet Gynecol Scand, 2011.PMID 21707554
14. [14]Visser GH, Ayres-de-Campos D FIGO consensus guidelines on intrapartum fetal monitoring: Adjunctive technologies Int J Gynaecol Obstet, 2015.PMID 26433402
15. [15]Ayres-de-Campos D, Spong CY, Chandraharan E FIGO consensus guidelines on intrapartum fetal monitoring: Cardiotocography Int J Gynaecol Obstet, 2015.PMID 26433401
16. [16]Viscarello RR, Copperman AB, DeGennaro NJ Is the risk of perinatal transmission of human immunodeficiency virus increased by the intrapartum use of spiral electrodes or fetal scalp pH sampling? Am J Obstet Gynecol, 1994.PMID 8141193
17. [17]Yeoh M, Ameratunga D, Lee J, et al. Simplifying the language of fetal monitoring Aust N Z J Obstet Gynaecol, 2019.PMID 30460717
18. [18]Alfirevic Z, Devane D, Gyte GM, et al. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour Cochrane Database Syst Rev, 2017.PMID 28157275
19. [19]Stål I, Wennerholm UB, Nordstrom L, et al. Fetal scalp blood sampling during second stage of labor - analyzing lactate or pH? A secondary analysis of a randomized controlled trial J Matern Fetal Neonatal Med, 2022.PMID 32233704
20. [20]Rørbye C, Perslev A, Nickelsen C Lactate versus pH levels in fetal scalp blood during labor--using the Lactate Scout System J Matern Fetal Neonatal Med, 2016.PMID 26004985