Back in September 2022, I wrote a blog post sharing my excitement about a randomised controlled trial that was underway in Ireland. The trial aimed to compare fetal blood sampling against digital fetal scalp stimulation as a second line test for fetal wellbeing when the CTG recording was abnormal (Murphy et al., 2022). The main outcome they were interested in was the caesarean section rate, with plans to also look at instrumental vaginal birth, decision to birth interval, mortality, Apgar scores, cord pH, admission to the nursery, neonatal encephalopathy and other neurological conditions, PPH, severe perineal trauma, perinatal mental health, and the acceptability of the procedure to women. They calculated that they would need 2,500 women recruited to provide a 90% chance of showing a 5-6% difference in caesarean section rates, if one existed. They expected it would take 3 years to recruit this many women.
I was excited about the trial, because it was a good question, and they aimed to include important outcome measures that have historically been overlooked in fetal monitoring research.
The final findings from the study have just been published and things did not go according to plan.
What happened?
The trial ended after one year, having recruited only 534 women, all giving birth for the first time. The decision to end the trial was based on lower than expected recruitment. Of the women who were recruited, 124 received second line testing for an abnormal CTG. [Note: this gives you an idea about just how common it is for women to experience a fetal heart rate pattern that is considered sufficiently abnormal to warrant intervention – 23% of this population.] 43 women accepted randomisation, with 20 being allocated to scalp stimulation and 23 to fetal blood sampling. For the other 81 women, most (65% or 53 women) had fetal scalp stimulation.
As you can tell – this fell well short of what they had planned. A study with 43 women is not going to be able to show statistically significant differences in anything, unless it is a common outcome and the difference is the size of a very large planet. Their pilot trial, done to understand how best to design the full study, randomised 50 women – so they combined the findings from this to help boost their numbers for the analysis.
What did they find?
When the data from both trials were combined, a significantly lower rate of caesarean section (for any reason) was found when fetal scalp stimulation was used (20% rather than 52%, p = 0.02). This was the only statistically significant difference of any of the trial outcomes. Acceptability was high for both tests at 95%.
It would be inappropriate to say the trial provides evidence that outcomes for babies and women are just as good between the two approaches. There is the hint of a suggestion that fetal blood sampling might, maybe, result in better outcomes, with lower rates of:
- low Apgar scores at 5 minutes of age (none vs 5%),
- cord blood acidosis (4.3% vs 15%),
- nursery admission (4.3% vs 10%), and
- neonatal encephalopathy (none vs 5%).
HOWEVER: The differences in baby outcomes related to one baby with a low Apgar score and neonatal encephalopathy. While randomised to scalp stimulation, this was not actually done, nor was fetal blood sampling used instead.
For women the rate of postpartum haemorrhage (8.7% vs 15%) and referral to a perinatal mental health professional (4.3% vs 10%) were also lower with fetal blood sampling. Why? I’m not sure… given the difference in the caesarean rate, which is associated with a higher risk for heavy blood loss and perinatal trauma, you would expect it to be the other way around.
The small sample size means we need to be careful when interpreting these findings. They may or may not reflect the truth of the matter and only an appropriately large trial will answer this question.
What happened?
When I first read the abstract of this paper, my first action was to scour the paper to work out why recruitment was such a challenge for this research project. There is a section in the strengths and limitations, explaining the trial start date had been delayed due to the pandemic. During the pandemic the birth rate at the hospitals involved in the trial fell, the caesarean section rate rose, and the use of fetal blood sampling fell from 10% to 3%, affecting the assumptions the sample size was based on.
Just after the trial began, NICE circulated a draft guideline advising that fetal blood sampling not be used. While the final guideline was later amended to remove this, it seems that obstetricians at the recruiting hospitals had already moved away from fetal blood sampling. This is reflected in the large number of recruited women who were not randomised. The trial design permitted obstetric staff to override the test allocation if they felt it was clinically justified. When this was the case, fetal scalp stimulation was the preferred choice.
What does this mean?
The trial provides a live demonstration of how powerful guidelines are in clinical practice. Ironically, the desire to follow professional guidance due to limited evidence about fetal blood sampling ultimately sabotaged efforts to generate the required evidence. This is a perfect illustration of how we ended up with many of the routinised interventions used having either no evidence to support them, or even evidence they are not effective.
The trial suggests that further research to answer the question of whether digital fetal stimulation is an appropriate second line test is warranted. The findings suggest that maybe the reduced caesarean section rate might come at the cost of worse outcomes for the baby. We really do need to know whether fetal stimulation should be used when the fetal heart rate pattern is abnormal before it continues to spread through practice. (Or we could abandon CTG monitoring completely and replace it with something that works – but that seems like it remains a long way off being achieved.)
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References
Murphy, D. J., Shahabuddin, Y., Yambasu, S., O’Donoghue, K., Devane, D., Cotter, A., Gaffney, G., Burke, L. A., Molloy, E. J., & Boland, F. (2022, Oct 4). 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, 23(1), 848. https://doi.org/10.1186/s13063-022-06794-9
Yambasu, S., Boland, F., O’Donoghue, K., Curran, C., Shahabuddin, Y., Cotter, A., Gaffney, G., Devane, D., Molloy, E. J., & Murphy, D. J. (2025, Jan 9). Digital Foetal Scalp Stimulation Versus Foetal Blood Sampling to Assess Foetal Well-Being in Labour: A Multicentre Randomised Controlled Trial. BJOG, in press. https://doi.org/10.1111/1471-0528.18068
Categories: CTG, New research, Perinatal brain injury
Tags: FBS, fetal blood sampling, Fetal stimulation, guidelines, Ireland, lactate, pH, RCT
Birth Small Talk 
Hi Kirsten, you know my question already. Any information about the baby that did badly in terms of neonatal interventions?
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“The baby in the dFSS group with the low Apgar score, neonatal encephalopathy, and an abnormal neurological examination at discharge was the baby of the participant who did not receive the allocated intervention. Labour had continued for several hours following randomisation, resulting in a difficult AVB and poor condition of the baby at birth. The baby had a normal neurological examination at 3 months of age.” I would bet money on early cord severance, though they don’t specifically describe this.
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