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ABSTRACT & COMMENTARY
Which Method Is Best for Assessing Fetal Well-Being During Labor?
July 1, 2025 8 minutes read
By Ahizechukwu C. Eke, MD, PhD, MPH
Synopsis: Although this study began as a randomized controlled trial and did not show a statistically significant difference between groups for the primary outcome, pooled analysis via a meta-analysis incorporating prior pilot data suggested a potential reduction in cesarean delivery with digital fetal scalp stimulation (dFSS) compared to fetal scalp blood sampling. Secondary maternal and neonatal outcomes were similar between the two groups, both procedures were well-tolerated, and clinicians showed a clear preference for dFSS.
Source: Yambasu S, Boland F, O’Donoghue K, et al. Digital foetal scalp stimulation versus foetal blood sampling to assess foetal well-being in labour: A multicentre randomised controlled trial. BJOG. 2025;132(5):557-564.
Fetal assessment during labor is critical for timely identification of intrapartum hypoxia and prevention of adverse neonatal outcomes, including metabolic acidosis, neurologic injury, and stillbirth.1,2 Two commonly used secondary methods to evaluate fetal well-being following a non-reassuring fetal heart tracing (FHT) are fetal scalp blood sampling (FBS) and digital fetal scalp stimulation (dFSS).3 FBS is a biochemical test involving the collection of capillary blood from the fetal scalp during labor to assess pH or lactate levels, parameters that serve as direct indicators of fetal acid-base status and, thus, metabolic well-being.3 In contrast, dFSS is a bedside clinical maneuver in which a digital (finger) stimulus is applied to the fetal scalp through the dilated cervix; a prompt acceleration in fetal heart rate is interpreted as evidence of intact neurological and acid-base function.3
In the United States, intrapartum electronic fetal monitoring (EFM) is near-universal, with more than 85% of laboring patients undergoing continuous FHT.4 While dFSS commonly is used in U.S. labor and delivery units because of its simplicity, noninvasiveness, and lack of equipment requirements, FBS is not used in the United Staes because of concerns regarding its invasiveness, operator dependency, and lack of U.S. Food and Drug Administration approval for lactate analysis.5 Despite widespread EFM use, the incidence of birth asphyxia remains a public health concern, where approximately two to three per 1,000 live births in high-income countries are complicated by hypoxic-ischemic encephalopathy (HIE) and intrapartum stillbirths occur in one to two per 1,000 deliveries, underscoring the limitations of current monitoring strategies.6,7
The clinical utility of FBS vs. dFSS remains a subject of ongoing debate, particularly in terms of diagnostic accuracy, safety, feasibility, and effect on obstetric outcomes. FBS, although considered the gold standard for intrapartum acid-base assessment, is associated with procedural limitations, including technical difficulty in sampling, need for cervical dilation of at least 3 cm to 4 cm, ruptured membranes, and sufficient fetal descent.8 Moreover, the invasiveness of FBS raises infection concerns, especially in populations with maternal human immunodeficiency virus (HIV), hepatitis B/C, or herpes simplex virus, leading many clinicians to avoid its use in such contexts. In contrast, an acceleration of the fetal heart rate following dFSS indicates that the likelihood of fetal acidosis (pH < 7.20) is approximately 2%.9
Meta-analyses of four fetal stimulation tests demonstrated that all were effective in predicting the presence or absence of fetal acidemia, with dFSS showing the highest positive predictive value and the lowest likelihood of acidemia when the test was negative. FBS also performed well, with a positive likelihood ratio of 8.54 and a negative likelihood ratio of 0.12, supporting its continued use as a reliable but more invasive alternative.9
Nonetheless, while dFSS provides a qualitative assessment and may reduce unnecessary interventions, it lacks the objective biochemical data of FBS, which may be crucial in high-risk or equivocal clinical scenarios. Based on these data, a nuanced comparison of these two modalities, factoring in their diagnostic performance, implementation context, and influence on perinatal outcomes, is necessary to optimize fetal surveillance and inform obstetric decision-making during labor. This need formed the rationale for the study conducted by Yambasu and colleagues.10
This study was a multicenter, parallel-group randomized controlled trial (RCT) conducted across maternity hospitals in Ireland, designed to compare dFSS with FBS as second-line assessments of fetal well-being during labor in women with abnormal FHT.10 Recruitment was restricted to nulliparous women with singleton, cephalic pregnancies at ≥ 37 weeks of gestation who required further evaluation because of non-reassuring FHT. Key exclusion criteria included multiparity, known contraindications to FBS (such as infection risks or incomplete cervical dilation), inability to understand English, < 18 years of age, and clinician judgment that urgent intervention was required.
To facilitate recruitment, patients were provided with trial information prenatally and enrolled with written informed consent. Randomization occurred only if second-line testing was warranted during labor. Allocation concealment was maintained through a secure, automated system. Although participant and clinician blinding were not feasible, outcome assessment for primary and secondary endpoints was performed blinded to treatment allocation.10
The primary outcome was the rate of cesarean delivery, while secondary outcomes included rates of assisted vaginal birth, spontaneous vaginal delivery, indications for operative delivery, adverse perinatal outcomes (e.g., neonatal encephalopathy, Apgar scores < 7 at five minutes, cord pH < 7.0, base excess < -12.0), maternal complications (e.g., obstetric anal sphincter injury, hemorrhage), and procedural outcomes such as decision-to-delivery interval. The trial employed a 1:1 randomization ratio between the dFSS group and the FBS group.
The sample size was calculated to detect a 5% to 6% absolute difference in cesarean delivery rates (with an expected rate of approximately 20% in the dFSS group), providing 90% power at a two-sided alpha of 0.05 with 1,250 participants per arm. However, because of slow recruitment and changing clinical practices, the trial was stopped early.
Statistical analysis was conducted using intention-to-treat principles. Logistic regression models were used for comparisons, and outcomes were reported as odds ratios (ORs) with 95% confidence intervals (CIs). A planned meta-analysis incorporating prior pilot RCT data also was performed to increase statistical power and explore pooled effect estimates.
A total of 534 women consented to participate; however, only 124 ultimately required a second-line test, and just 43 (34.7%) were randomized, with 20 to dFSS and 23 to FBS. The rate of cesarean delivery was 40.0% (8/20) in the dFSS group and 47.8% (11/23) in the FBS group (OR, 0.73; 95% CI, 0.22 to 2.44; P = 0.61). Although this difference was not statistically significant, a meta-analysis combining these results with prior pilot data (n = 50) showed a significantly lower cesarean delivery rate in the dFSS group: 28.9% vs. 50.0% (OR, 0.41; 95% CI, 0.17 to 0.96; P = 0.04).
Secondary outcomes did not differ significantly between the two groups. Adverse outcomes, such as cord pH < 7.00, occurred in 15% of dFSS vs. 4.3% of FBS cases (OR, 3.69; 95% CI, 0.34 to 39.84; P = 0.28). Procedural issues were uncommon: one inconclusive dFSS test and two failed FBS attempts. Overall, both tests were highly acceptable to patients, with 95% to 100% reporting no concerns, and the data suggest a strong clinician preference for dFSS.
Commentary
This multicenter RCT comparing dFSS to FBS as second-line tests for assessing fetal well-being during labor found no statistically significant difference in cesarean delivery rates between the two approaches when analyzed alone; however, a meta-analysis incorporating prior pilot data suggested a potential reduction in cesarean delivery with dFSS. Both methods demonstrated comparable safety profiles, with no significant differences in adverse maternal or perinatal outcomes and were highly acceptable to patients.
Importantly, the trial revealed a notable clinician preference for dFSS, likely influenced by its simplicity, noninvasiveness, and alignment with evolving clinical guidelines that increasingly discourage the routine use of FBS because of limited supporting evidence. Although the trial was underpowered because of lower-than-expected enrollment, its findings suggest that dFSS may offer a practical and patient-centered alternative to FBS in settings where clinical equipoise exists. The results of this trial contribute to the growing body of evidence suggesting that dFSS may serve as a clinically useful, lower-intervention alternative to FBS in the assessment of fetal well-being during labor.
These findings are clinically important given that the majority of intrapartum cesarean deliveries are performed as the result of concerns over non-reassuring FHTs, many of which are false-positives.3 A diagnostic adjunct such as dFSS, that can reduce unnecessary operative deliveries without compromising neonatal outcomes, is of significant value.
The study also highlights the potential effect of clinician preference, workflow practicality, and real-time decision-making in labor and delivery floors, where time-sensitive assessments are needed. FBS, while offering quantitative data on fetal acid-base status, remains more invasive, technically demanding, and time-consuming, factors that may limit its utility in urgent or equivocal cases.11 Therefore, even in the absence of definitive superiority, dFSS may be favored in clinical practice because of its ease of use and favorable risk-benefit profile.
The broader clinical implications are especially relevant in the context of changing guidelines and real-world practice patterns. Recent revisions by the United Kingdom’s National Institute for Health and Care Excellence (NICE Guidelines) have moved away from recommending routine use of FBS, citing insufficient evidence, while supporting dFSS when suspicious cardiotocography patterns are present.12 Similarly, the American College of Obstetricians and Gynecologists guidelines acknowledge dFSS as a practical bedside assessment that may help reduce false-positive FHT interpretations.5 This shift is crucial, since more than 85% of labors in the United States use continuous electronic fetal monitoring, a modality known for its high sensitivity but poor specificity, leading to unnecessary interventions.4 Nonetheless, dFSS, by eliciting a reassuring fetal heart rate acceleration, provides a fast, noninvasive way to assess fetal neurological integrity and acid-base status without the procedural risks of FBS. However, given that dFSS remains an observational test and does not provide direct biochemical evidence, its use should be supported by clinical judgment.
Until larger, adequately powered trials are completed, these findings suggest that dFSS may serve as the preferred second-line test for many patients, balancing diagnostic utility with patient safety and procedural feasibility.
Ahizechukwu C. Eke, MD, PhD, MPH, is Associate Professor in Maternal Fetal Medicine, Division of Maternal Fetal Medicine, Department of Gynecology & Obstetrics, Johns Hopkins University School of Medicine, Baltimore.
References
1. Tsikouras P, Oikonomou E, Bothou A, et al. Labor management and neonatal outcomes in cardiotocography categories II and III (review). Med Int (Lond). 2024;4(3):27.
2. Reynolds AJ, Murray ML, Geary MP, et al. Fetal heart rate patterns in labor and the risk of neonatal encephalopathy: A case control study. Eur J Obstet Gynecol Reprod Biol. 2022;273:69-74.
3. Murphy DJ, Devane D, Molloy E, Shahabuddin Y. Fetal scalp stimulation for assessing fetal well-being during labour. Cochrane Database Syst Rev. 2023;1(1):CD013808.
4. Cahill AG, Tuuli MG, Stout MJ, et al. A prospective cohort study of fetal heart rate monitoring: Deceleration area is predictive of fetal acidemia. Am J Obstet Gynecol. 2018;218(5):523.e1-523.e12.
5. [No authors listed]. ACOG Practice Bulletin No. 106: Intrapartum fetal heart rate monitoring: Nomenclature, interpretation, and general management principles. Obstet Gynecol. 2009;114(1):192-202.
6. Nelson KB, Grether JK. Potentially asphyxiating conditions and spastic cerebral palsy in infants of normal birth weight. Am J Obstet Gynecol. 1998;179(2):507-513.
7. Lawn JE, Blencowe H, Waiswa P, et al. Stillbirths: Rates, risk factors, and acceleration towards 2030. Lancet. 2016;387(10018):587-603.
8. 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;2015(5):CD006174.
9. Skupski DW, Rosenberg CR, Eglinton GS. Intrapartum fetal stimulation tests: A meta-analysis. Obstet Gynecol. 2002;99(1):129-134.
10. Yambasu S, Boland F, O’Donoghue K, et al. Digital foetal scalp stimulation versus foetal blood sampling to assess foetal well-being in labour: A multicentre randomised controlled trial. BJOG. 2025;132(5):557-564.
11. Carbonne B, Pons K, Maisonneuve E. Foetal scalp blood sampling during labour for pH and lactate measurements. Best Pract Res Clin Obstet Gynecol. 2016;30:62-67.
12. National Institute for Health and Care Excellence. Fetal monitoring in labour: [A] Evidence review for fetal blood sampling. Published December 2022. https://www.nice.org.uk/guidance/ng229/evidence/a-fetal-blood-sampling-pdf-11313941294
Although this study began as a randomized controlled trial and did not show a statistically significant difference between groups for the primary outcome, pooled analysis via a meta-analysis incorporating prior pilot data suggested a potential reduction in cesarean delivery with digital fetal scalp stimulation (dFSS) compared to fetal scalp blood sampling. Secondary maternal and neonatal outcomes were similar between the two groups, both procedures were well-tolerated, and clinicians showed a clear preference for dFSS.
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