Episode 125 Fetal Blood Sampling

What is Fetal Blood Sampling? How did we do it , and why I think it should it be abandoned if you haven't already stopped this procedure?

Want to know more?
https://www.nice.org.uk/guidance/gid-ng10174/documents/draft-guideline
https://obgyn.onlinelibrary.wiley.com/doi/full/10.1111/aogs.12416
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006174.pub3/full

https://www.nice.org.uk/guidance/cg190/ifp/chapter/if-electronic-monitoring-is-needed#fetal-blood-sampling

Thank you all for listening, My name is Florence Wilcock I am an NHS doctor working as an obstetrician, specialising in the care of both mother and baby during pregnancy and birth. If you have enjoyed my podcast please do continue to subscribe, rate, review and recommend my podcast on your podcast provider.
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Transcript

Episode 125 Fetal Blood Sampling

Florence: [00:00:00] Hello, my name's Florence. Welcome to the obs Pod. I'm an NHS obstetrician hoping to share some thoughts and experiences about my working life. Perhaps you enjoy, call the midwife, maybe birth fascinates you, or you'll simply curious about what exactly an obstetrician is. You might be pregnant and preparing for birth.

Perhaps you work in maternity and want to know what makes your obstetric colleagues tick or you want some fresh ideas and inspiration, whichever of these is the case. And for that matter, anyone else that's interested, the obs pod is for you.

Episode 1 25, fetal Blood Sampling. When I was working on maternity experience with my good friend Gill Phillips on [00:01:00] whose shoes scenarios, one of my favorite scenarios was called Changing Times. I've referred to it previously in the podcast. It asked what things we do. That may appear odd or outdated in the future.

On the labor ward this week, we were discussing fetal heart monitoring, a very controversial topic, which I've discussed in previous episodes, and fetal blood sampling cropped up as part of the conversation and the midwife that I was talking to who is an experienced band, six midwife. She's been a midwife for some years, said, I've never seen a fetal blood sample, and this stopped me in my tracks and made me think, [00:02:00] and hence today's episode.

How come she's never seen a fetal blood sample? Something that for me was a daily part of my bread and butter. It was a technique, a skill I needed signed off during my training, and it was something on which we based many decisions and it's something we no longer do, or at least not at my hospital. And when this cropped up at the British Intrapartum Care Conference.

That I went to a month or so ago. It's also true that this is a thing of the past for many hospitals. However, I suspect it is not a thing of the past for everyone, whether that's some units in this country [00:03:00] or other units around the world, and therefore, I thought it was worth thinking about it on today's episode

why is it that I believe that some units may be doing fetal blood sampling? Well, it's because it's been in the nice guidance, even though it's been controversial for a significant length of time. We probably haven't done a fetal blood sample in my hospital for more than five years, but it's only in the advent this year of a new.

Nice. National Institute for Health and Care Excellence guideline that went out for consultation in July, 2022. That was the first time that the NICE guidance has specifically said, do not offer fetal blood sampling in labor to assess [00:04:00] fetal wellbeing in brackets 2022. This is a new recommendation. Okay, let's go back to the beginning.

What is a fetal blood sample? It is a capillary blood sample taken from the scalp of the baby during labor and analyzed to look at pH , why PH?. Well, because if you think. A capillary blood sample. It's not actually very helpful at assessing oxygen levels. The blood in your capillaries has already had oxygen exchange.

It's not arterial blood. It's not telling us how much blood the baby received, and it's also not venous blood. It's not telling us what is the situation when the baby's used things up. So we look at pH, the acidity of the. And that's because [00:05:00] depending on how the baby is coping with labor will depend on whether it's using aerobic metabolism that is using oxygen to break down sugars into energy, or whether it's using anaerobic metabolism.

That's the sort of thing you get when you exert yourself and you build up lactic acid in your muscles. You haven't been able to get sufficient oxygen to the muscles and your blood therefore becomes more acidic because of the buildup of lactic acid. So there is a question, first of all, whether we should have been looking at pH or whether you look at lactate, the derivative of lactic acid in the first place.

But let's just push that to one side. Why would we use it? [00:06:00] Well, this used to be used because when we were concerned about a baby's wellbeing in labor, we know that CTG cardiograph interpretation has poor sensitivity and specificity. That means that half the time the baby's heart rate looked abnormal, it was actually not correct, and we.

might Take intervention unnecessarily. We get a false positive, as it were. We would think the baby was in trouble. We would need to intervene, possibly doing a cesarean or an assisted vaginal birth, and actually the baby would be fine. So the idea of doing a fetal blood sample was an attempt to give us additional information about the wellbeing of the baby on which to base our decisions.

It's not easy to get a sample from the scalp of a baby [00:07:00] during labor. Let me just talk it through. It's a tricky procedure and that's just for me, the doctor and the midwife, let alone the poor woman. How do we do it? Well, it involved getting the woman on her side. Often with a midwife holding her leg up or a stirrup on the side of the bed holding her leg up, and we would insert a type of speculum called an amniscope into the vagina, and then remove the central bit of the speculum to enable us to see the baby's head.

Of course, there's not a lot of light when you're looking up a. The birth canal towards a baby's head, so we would need a light. We would be shining a torch so that we could see more clearly. Then we'd use an instrument to hold a swab and swab the head [00:08:00] to clean off any amniotic fluid or maternal blood.

Then we'd take another swab and put a little bit of Vaseline and smear it on the scalp. This is so that the blood would bleb up into little beads. Droplets that we'd be able to collect more easily, then we'd use a cold spray similar to that used by the anesthetist to test the block on their epidural or spinal, and that would numb things.

At least that's what we said, and that's what we thought, but I'm not sure whether that's true. Then we would apply pressure with a small blade, a little bit like when you have a finger prick blood test to check perhaps your blood glucose. Or if you give blood, they do a small pin prick blood test to check your blood count.

Then we would have to delicately hold a tiny thin capillary tube to collect the blood. We would need two capillary [00:09:00] tubes full, ideally, so that we could believe the sample, and also because the machine would often swallow the samples that we'd painstakingly collected. The blood needed to flow fairly freely as if it was too slow, it would clot as we were collecting it.

Once we'd collected the samples, we would put a little flee, a tiny magnet inserted into the tube and moved along the tube by externally moving another magnet up and down to prevent clotting while we ran to the machine. Then we would put a small little plastic gadget called a clot catcher. Over the edge of the tube and feed it into the machine and get an answer.

So the midwife would run off with the samples while the doctor pressed a swab on the top of the head of the baby to clot the spot where we'd made the little pin prick and wait anxiously for the result. , if you think [00:10:00] what I've described is already complicated enough, then add in the fact that you've got a woman.

Usually a partially dilated cervix so that the view of the baby's head and where you've made your little cut could disappear at any point midway through proceedings. You've also got a woman in pain who can't keep still, and she's finding it very uncomfortable. You might have a baby with lots of hair, so it's almost impossible to get a sample into the capillary tube.

Then you might have amniotic fluid flowing everywhere. Difficulties with a torch so that we can't see properly. And then there's getting the position right? I learned early on in my career, it's important to put a hat on before you start trying to take fetal blood sample because. As you lean over and peer up your amniscope up the birth canal [00:11:00] towards the baby's head, you don't want your head to be flopping and dipping in amniotic fluid and blood and all the other things that might be on the bed as you go.

You've also then got very fine glass tubes, so fine that they might snap and shatter as you hold them, and that's certainly happened to me in the. And then of course, backache from leaning over. I remember being very excited when we got proper kits. Kits with an integrated light source, much better plastic, safer capillary tubes that were longer and didn't shatter, and our success rate was much higher.

Why am I worried about success rates? Well, the chances your sample would clot. Or be insufficient. If you don't fill the whole tube or way beside you arrive at the machine, which will be calibrating while you [00:12:00] stand helpless with your precious sample under pressure, worrying it's clotting. In the meantime, while you're waiting, if you can't get a sample or if you can't get a result from a sample and you've decided the cardiograph, the heartbeat, trace merits.

Because you are concerned about the wellbeing of that baby, then you've only got one option. If you fail to get a result from your sample, then you need to deliver the baby. So we've got an incredibly tricky procedure with all sorts of pitfalls. If we decide to do it, we're committed. We have to take action.

What if we do get an. What if we do get results? What do they mean? What then? If the baby had a pH of 7.25 to 7.35, we would be [00:13:00] happy with that. That meant the baby was absolutely fine. It was completely normal. Yes. I know that's like, that's more acidic than a normal adult pH would be, but that is normal for a baby in.

Labor is a stress. If the pH result was between 7.2 and 7.25, that would be concerning. That would mean a borderline result, and the nice guidance would be that there should be a repeat in less than 30 minutes if still indicated or. If the ctg, the fetal heartbeat trace deteriorated. Let's pause there a moment.

Okay. You faffed around. You've very, with great difficulty, got your blood sample, and then you get that borderline result. [00:14:00] Remember, you've tried to take two samples so that you know it's accurate. You need to have another sample in less than 30 minutes. It could take you 30 minutes to do the thing in the first place.

There's even been published data that I remember about it, taking 15 to 20 minutes to take a sample, so you've almost got to start straight away before you've finished the first one. Got to continue. Let's go back. To our 7.25 to 7.35. That was normal. But if we're still concerned about the ccg, we should repeat it in an hour.

That could be useful, and that's where I used to be a positive advocate of fetal blood sampling because if I had a woman who [00:15:00] could progress in her labor in that time and getting a normal result, Would mean that I wouldn't need to intervene. I could then examine her again in an hour if the heartbeat concerns remained the same and I could use the fetal blood sample to reassure myself and stave off intervention In the intervening time, maybe she'd become fully dilated or in the intervening time.

The fetal heartbeat trace would become less concerning, so I could use the fetal blood sample to avoid doing a cesarean or an assisted vaginal birth safely. Let's now consider what if the result isn't normal? Abnormal is defined as pH of less than 7.2. And that [00:16:00] requires what we call category one delivery, and I've talked about that in my episode on cesareans.

That means that ideally, from decision to delivery, the birth of the baby should be 30 minutes or less, ideally. So pH of 7.20 means action. Action straight away, whether that be cesarean or assisted vaginal birth, depending on the stage of. And I think it's for that reason that if we are concerned about the fetal heartbeat tracing, it was always said that if you couldn't get a result, you should intervene.

Now, I mentioned lactate earlier and we didn't used to use lactates when I did fetal blood samples, but I can see on the internet, if you look, there are many hospitals guide lines on fetal blood sampling that do include descriptions of lactate, and there is some interesting [00:17:00] data on the Cochrane database about the use of lactate versus pH.

We used to use something called base excess. Again, the base excess is something that counteracts the acidity of the baby's blood. It tells you again about whether it's. Aerobic metabolism using oxygen or anaerobic without oxygen. If the base success is high, then the baby's more acidic, and it means the baby's compensating for the stressful situation it's in, and it's having to produce lots of base to counteract the acidity.

So base excess of more than eight was considered. Now, the cutoff we used to use of 7.20 is interesting because in actual fact, what we're trying to reduce [00:18:00] is hypoxic injury, so lack of oxygen causing damage to the baby's brain or other organs. This can result in some cases in cerebral palsy, long-term damage.

But if you look at data published about outcomes of babies and the association with cerebral palsy, there's lots of data that demonstrates above a pH of 7.0. You are very unlikely to get damage that causes cerebral palsy. So by choosing a threshold of 7.20. And remember, pH is a logarithmic scale, so it's exponential.

So the difference between 7.0 and 7.2 is massive. By choosing [00:19:00] 7.2 or less than 7.2, we're giving ourselves a huge margin of error to intervene early and prevent long term consequences. . So the rationale for doing fetal blood samples was to know when to safely intervene and when to step back and do nothing.

And the idea was that if you did fetal blood samples as an adjunct to your fetal heart monitoring, you would be able to reduce intervention and for a long, , I was an advocate of fetal blood sampling. I admit it. It made sense. I could understand why we were making decisions on that basis, and I remember the moment at which the tide started to turn, and I remember a colleague [00:20:00] at another trust who stood up and talked about fetal blood sampling and why it wasn't a good.

And put up a very emotive picture projected as part of his talk of essentially a kitchen knife poised over the head of a baby. And I remember arguing and feeling very uncomfortable with that image. It was meant to shock and it. So why is it now that I'm a firm believer that fetal blood sampling should be a thing of the past?

If you look at the latest draft guidance from nice, there's some explanation as to their rationale. They have said that there is recent but limited evidence that [00:21:00] fetal blood sampling does not improve outcomes for women and. Compared to fetal heart monitoring alone and that fetal blood sampling may actually do harm, it may increase the proportion of babies with low Apgar score less than seven at five minutes, possibly because of a delay in expediting birth to allow the fetal blood sampling to be carried out.

Remember, I've described it's quite a tricky procedure it takes time , the committee agreed it was difficult to define whether this outcome was harm or a benefit, but they concluded that the time taken to carry out fetal blood sampling can delay appropriate expedition of birth, and that can be an unpleasant procedure for the mother, especially in the absence of an effective epidural.

The committee therefore [00:22:00] agreed that the risks of fetal blood sampling were not balanced by the benefits. And then it mentions, there's ongoing research comparing fetal scalp stimulation. That is when you do a vaginal examination and touch the baby's head, the baby responds with its heart rate, with fetal blood sampling or maternal or fetal outcomes

and they noted that there's not going to be a completion of that research until the end of 2024, and then it may need to be reviewed again. I find this very interesting because they haven't concluded what I might have concluded, which is I'm not sure how accurate the samples were. I mean, we're taking a drop of blood hoping it's not mixed with amniotic fluid [00:23:00] and maternal blood.

And also we're expecting the blood on the scalp of the baby that's being pushed and pressed down the birth canal to reflect the blood results of the whole baby. If I constrict my hand around my. a bit like when you have a blood pressure done in the antenatal clinic gradually what happens is blood will collect in the capillaries in my fingers.

If I take after some time a blood test from my fingertip, will that be the same as if I took a blood? from a toe that was not being pressed on or constricted. To me it doesn't make [00:24:00] sense that it would. So my worry and the worry that originally was put forward by my colleague who was anti fetal blood sampling was that it just simply wasn't accurate.

And I've included in the program notes a paper about the pathophysiology of fetal blood samples and how they may or may not accurately reflect what is going on in the baby. This brings me to my Zesy bit. My zesty bit is if you are a professional working in maternity services. , has your maternity service stopped doing fetal blood sampling?

If not, why not draw people's attention to the latest nice guidance? Draw [00:25:00] people's attention to the fact that there isn't good evidence for this invasive procedure. Why am I worried that people might still be doing. Well, when I looked at a few things to explore this topic in a bit more detail, up popped a number of hospitals current guidelines, which include fetal blood sample.

So I have reason to believe that there are many hospitals up and down the country that are still performing this procedure. I understand it takes. for guidance to be implemented, and this is new draft guidance that's just come out this summer. But I would suggest that this change in guidance is long overdue and we really [00:26:00] need to get on with implementation.

We owe it to mothers and babies to do so as quickly as possible If. A pregnant woman listening to this or expectant parent, maybe ask at your antenatal classes or appointments, does the maternity unit, you are going to do fetal blood samples, and if so, form a view, educate your. Do you or do you not want to consent to a fetal blood sample?

Put it in your birth plan. Maybe draw people's attention to the fact that you are or aren't happy to do this. It isn't a very pleasant procedure [00:27:00] and. I genuinely thought I was doing the right thing, and I genuinely did take what I felt were good decisions. As a result, I now feel apologetic to those women that I put through that experience during the birth of their children.

So don't accept that. It's something you have to. Know that there may be consequences of your actions, so if staff are worried about your baby, it may mean more chance of a cesarean or an assisted vaginal birth, but it may not, and it may mean not relying on something that actually is questionable and inaccurate.

At a crucial moment during your birth. [00:28:00] I very much hope you found this episode of the obs Pod. Interesting. If you have, it'd be fantastic if you could subscribe, rate, and review on whatever platform you find your podcasts, as well as recommending the obs pod to anyone you think might find it interesting.

There's also tons of episodes to explore in my back catalog from clinical topics, my career and journey as an obstetrician and life in the nhs. More generally, I'd like to assure women I care for that. I take confidentiality very seriously and take great care, not to use any patient identifiable information unless I have expressly asked the permission.

Of the person involved on that rare occasion when it's been absolutely necessary. If you found this [00:29:00] episode interesting and want to explore the subject a little more deeply, don't forget to take a look at the program notes where I've attached some links. If you want to get in touch to suggest topics for future episodes, you can find.

At the obs pod on Twitter and Instagram, and you can email me the obs pod gmail.com. Thank you for listening.