Should fetal blood sampling become a thing of the past?

Collecting a sample of blood from the fetal scalp during labour has been around for as long as CTG monitoring has existed. Erich Saling reports that it was first used on June 21, 1960 – and the following day successful blood sampling from the buttock a breech presenting fetus was achieved. He said at the time that monitoring the fetal heart rate alone would always be an inadequate approach:

The situation in cardiotocography can be compared with vocalization of monkeys in the jungle; when danger is imminent they always scream. When there is a threat of hypoxia, the fetal heart rate is almost always suspicious or pathological. But monkeys scream much too often; especially when there is no real danger at all.

The solution he proposed was to monitor fetal pH levels, as he believed this more closely reflected fetal oxygen status.

Fetal blood sampling has shifted in and out of vogue, with varying rates of use in different countries – while the use of CTG monitoring has risen, risen, and remained consistently high everywhere. There is once again current debate about whether fetal blood sampling should be relegated to the past – or remains a vital part of modern clinical practice. Garabedian & Girault (2025) have provided an excellent summary of the issues in their review paper, and I summarise their key points here:

Do fetal scalp pH levels predict cord blood pH levels? Not very well. When the fetal blood pH was low, only 3.9% of babies had a low cord pH.
Have the appropriate cut off points been determined for fetal blood lactate testing? No. This remains under debate.
Does research show a difference in outcomes between pH and lactate testing of fetal blood? The failure rate was higher with pH testing, but no other differences. The rate of agreement between pH and lactate when measured on the same samples is less than ideal, with almost one in three test results being discordant (normal in one, abnormal in the other).
Is there evidence from randomised controlled trials? There are three – the first in 1979, the Flamingo trial in 2021, and the Yambasu trial in 2025. None provide compelling evidence about, well, anything much. The two most recent trials were ended early due to low rates of recruitment.
Are there other concerns? Fetal blood samples can be contaminated with maternal blood, amniotic fluid, or meconium; the pressure of the amnioscope can itself alter scalp circulation and modify results; the time taken to perform the test and get results might delay intervention while fetal deterioration continues; and point-of-care testing machines can be unreliable.

The authors conclude that:

FBS should not be banned from our practices, but rather reserved for specific indications where additional metabolic assessment may guide clinical decision-making.
p. 5

The paper provides a good overview of the topic – and I consider it essential reading for anyone who uses fetal blood sampling in their practice. I have two remaining observations to make.

First, given the current state of evidence about fetal blood sampling, any research group who thinks that continuous lactate monitoring is going to provide the solution to all our problems either doesn’t have a firm grasp on the evidence, or is deliberately ignoring it. There’s no firm ground on which to build this as an “advance” in fetal monitoring approaches.

Second, there’s no firm ground for fetal heart rate monitoring either. What I see reflected back at me in this paper is the equivalent of more than sixty years of trying to catch pixies as they whizz past. We could acknowledge the possibility that the theoretical basis of fetal heart rate AND pH monitoring is fundamentally flawed and we need to look for other biological parameters that could actually work. Instead, far too many researchers and tech developers continue to run about energetically shouting “I almost got it this time!”.

You’ve read the blog posts, but still want more? Wish you could find details summaries of all the evidence in the one place? Want to connect with a growing tribe of people working to solve the fetal monitoring problem?

The Fetal Monitoring Academy is a HUGE resource library covering just about every aspect of fetal monitoring research, with expert analysis and critique so it is easy to understand. New content is added regularly in response to requests from Academy members – so you will find exactly what you are looking for. You also get:

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If you are a maternity professional, doula, educator, researcher, or simply a birth nerd who wants to know more – the Fetal Monitoring Academy is perfect for you.

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References

Garabedian, C., & Girault, A. (2025, Oct). Should fetal blood sampling still be a part of monitoring during labor in the modern era ? Journal of Gynecology, Obstetrics, & Human Reproduction, 54(8), 102991. https://doi.org/10.1016/j.jogoh.2025.102991

Saling, E. (2006). Fetal blood analysis during labour. American Journal of Obstetrics & Gynecology, 194(3), 896-899. https://www.ajog.org/article/S0002-9378(05)00785-4/fulltext