Episode 121 Small Baby

I can't believe I have managed to neglect the topic of a small baby up to this point especially given Episode 29 Big baby is now my most popular episode. Join me to rectify this omission as I discuss what we think about when a baby is small , and what do we mean by small anyway?

Want to know more?
https://www.isuog.org/static/b2aa3fb4-031e-4d84-b7246d613a466884/ISUOG-Practice-Guidelines-diagnosis-and-management-of-small-for-gestational-age-fetus-and-fetal-growth-restriction.pdf
https://www.rcog.org.uk/media/t3lmjhnl/gtg_31.pdf
All about obstetric dopplers:
 https://obgyn.onlinelibrary.wiley.com/doi/10.1111/tog.12152
The InterGrowth study:
https://obgyn.onlinelibrary.wiley.com/doi/10.1111/tog.12281

Information for parents:
 https://www.rcog.org.uk/for-the-public/browse-all-patient-information-leaflets/having-a-small-baby/
https://www.tommys.org/pregnancy-information/pregnancy-complications/fetal-growth-restriction-intrauterine-growth-restriction

Thank you all for listening, if you have enjoyed my podcast please do continue to subscribe, rate, review and recommend my podcast on your podcast provider. Do explore my back catalogue of episodes and feel free to get in touch to suggest topics, I love to hear your thoughts and ideas. If you have found my ideas helpful please recommend theobspod to others who may be interested in exploring all things pregnancy and birth. You can find out more about me on Twitter @FWmaternity & @TheObsPod as well as Instagram @TheObsPod and email me on TheObsPod@gmail.com please check out #MatExp matexp.org.uk for ideas about how to improve maternity experience.
  My beautiful artwork is thank to Anna Geyer www.newpossibilities.co.uk

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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Its easy to explore my back catalogue of episodes here https://padlet.com/WhoseShoes/TheObsPod I have a wide range of topics that may help you make decisions for yourself and your baby during pregnancy as well as some more reflective episodes on life as a doctor.
If you want to get in touch to suggest topics, I love to hear your thoughts and ideas. You can find out more about me on Twitter @FWmaternity & @TheObsPod as well as Instagram @TheObsPod and e...

Transcript

Episode 121 Small Baby

Florence Wilcock: [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 121. small baby. This week I was looking at my stats for my podcast I do every once in a while [00:01:00] just to kind of figure out what you are all listening to, what are the popular things? And this week, Big Baby, it's true, it's neck and neck with home birth, but it's actually edged ahead as my most popular episode.

This got me thinking. How come I haven't done an episode on a small baby? How remiss of me I'm 120 episodes in, I can't believe I haven't thought about it. Therefore, this week I'm gonna think a little bit about small babies to balance things up a bit. Many pregnancies where the baby is found to be small, may end up being cared for by specialist fetal medicine consultant.

An expert in scanning and dealing with small babies. Just to be clear, I'm not one of them. I did do ultrasound [00:02:00] training, It's true, but I no longer scan on a regular basis, and I wouldn't hope to look after very, very small babies. So what I'm gonna discuss today is the way I an average obstetrician deal with.

Day to day. First of all, we need to think what counts as a small baby, and there are a few things to think about here. Typically, we're looking at babies on the 10th centile or less. That's the smallest 10% of babies. What do I mean by centile? Well, this is when we plot the baby on a centile chart. You may have seen these scan measurements on a chart.

Or charted when the midwife measures what we call the symphyseal fundal height, you know that measurement from the pubic bone to the top of the womb. That's done with a tape measure. At every [00:03:00] antenatal checkup, we will plot these measurements or scan measurements on a chart that tell us where 50% of babies will be the top 10% and the smallest 10%.

This measurement with a tape measure is a crude screening test for smaller babies, and we can use the measurements to decide if an additional scan is warranted. The other place you may have seen these Centile charts are if you've got an existing child, they're in your red book to show the growth and development of your baby through childhood up to age five, usually.

If we're using the 10th centile, by definition, 10% of babies will be categorized as small. Other descriptions you may hear doctors or midwives use are small for dates, SFD, or [00:04:00] small for gestational age sga. And you also may hear the expression, fetal growth restriction, fgr or intrauterine growth restriction, I U G R.

This is a bit different because growth restriction may not actually be a small baby. It might be, but it might be that the baby is actually what would be considered a normal size but hasn't reached its full potential, strictly speaking, to decide if the baby has growth restriction. We need more than one scan because we need to look at the growth over time.

any baby should track the centiles. In other words, on the chart, it should be growing in such a way that it runs parallel with the lines. It means it's maintaining its growth velocity. [00:05:00] In other words, it's growing at a stable rate. growth restriction is when a baby is no longer tracking. In other words, its growth rate has slowed down and we see the measurements start to cross the centiles.

An example of this might be a baby started out on the 50th centile where 50% of babies will be on one scan and on the next scan might be on the 15th centile. Now that's a considerable difference. in where it is overall, and that means the growth velocity or growth rate is reduced. That is what we mean by growth restriction.

And the reason I say these babies won't necessarily be small is because if your baby had the potential to be a nine pound baby genetically, and then your baby is actually. [00:06:00] Six pounds, it's growth restricted. Even though its overall weight may fall within the normal range. So let's consider at a checkup.

The midwife thought your bump was a little bit smaller than expected, and a scan confirms this. We'll then be trying to think what might the underlying cause be? There's a variety of things we might think about. The first thing is, is this baby, what we might call constitutionally small. Maybe you're very petite, maybe small babies run in the family.

It may be the baby is small, but consistently growing and in proportion. This baby genetically may be destined to be that weight. This baby's placenta is working perfectly. , this baby is perfectly healthy.[00:07:00] 

We do have to be a little bit careful with constitutionally small because there are questions about the size of babies in different ethnic groups. And the idea of customized growth charts has become extremely popular. The idea being that we shouldn't be measuring a baby from perhaps a South Asian background on a growth chart designed for Caucasian babies, however, we do need to be a little bit cautious with this,. because there's more recent evidence from a study called Inter Growth 21st Project, a large scale multi-country study that measured fetal growth of babies in the womb and at birth, [00:08:00] who discovered that 97% of variation in fetal growth is caused by factors unrelated to ethnicity.

And that unfortunately, by customizing growth charts for ethnicity, we could normalize suboptimal growth of these babies. There are actually a myriad of environmental, social, medical, and pregnancy conditions that make a difference rather than ethnicity. So we have to be a little bit careful when we think about constitutionally small 

in relation to ethnic background. Okay. We're not thinking this baby's constitutionally small. What are the other obvious explanations? One of the first questions we have to ask ourselves. Are the [00:09:00] dates correct? Remember in the episode on ultrasound scans, I talked about the importance of a dating scan at 12 weeks.

Most women who've booked in for early antenatal care will have had that booking dating scan, so we can be sure about their dates, but if women have booked later, maybe they didn't realize they were pregnant. or maybe they didn't have access to antenatal care. Then for those women, we need to think, are the dates correct or is this baby small

just because actually this woman is less pregnant than we thought she was. If the baby actually is small, then. There are two possible underlying reasons or we divide them into two. The first group is non [00:10:00] placental reasons. If you have a very small baby, we might check your blood tests for some of the common infections in pregnancy that might cause a smaller baby, such as CMV cytomegalovirus, or toxoplasmosis infection.

We may also look back at your genetic screening tests if you've had them, and repeat a top to toe anomaly scan to check for any differences in the way the baby's organs are formed as some babies that are small may have an underlying genetic issue or have had an infection in the womb. More common is the second group placental reason.

This can sometimes be called the rather alarming placental insufficiency. The idea is the placenta just isn't allowing this baby to reach its full [00:11:00] growth potential. It's not providing sufficient nutrients. The blood supply isn't good enough. Babies that have growth restriction in this way have some really smart adaptations to this situation.

The most important organ for the baby is the brain. So what does the baby do? It redistributes its blood flow to its brain to protect the brain, sometimes called brain sparing. So sometimes on the scan what we see is the head measurements are less affected than the tummy or thigh bone measurements.

That is the abdominal circumference and femur length. When I explain this to couples, this often raises the question, is your baby going to look weird or out of proportion when it's born? [00:12:00] But this isn't the case. All babies have a proportionately, bigger head than an adult. But it does mean when I'm looking at the measurements.

On the scan, this is something I need to consider, not just the overall baby's size, but what is happening with these individual measurements. We'll also look at the amniotic fluid around the baby because in the second half of pregnancy when growth issues are more common, the amniotic fluid is mainly composed of the baby's urine.

and one of the things that influences the amount of urine the baby's producing is whether or not the baby's kidneys are getting a good blood supply. If they are, you get normal levels of amniotic fluid. If they're not, then the fluid may be reduced, So reduced water around the baby [00:13:00] sometimes called oligohydramnios

is again, a sign that this is more likely to be placental insufficiency or a placental problem. We'll also look at some blood flow tests or dopplers. There are a number of different sorts of blood flow tests, and sometimes parents and midwives find these confusing at a 20 week scan the dopplers we measure are actually uterine artery dopplers.

That is the blood flow in the artery leading to the womb. Why would we be looking at that? Well, if you go back to my episode on the placenta, you'll remember that the placenta forms when the trophoblast that's some cells from the embryo. [00:14:00] Invade into the muscle of the womb and the uterine, the womb spiral arteries.

Smaller growth, restricted babies with a placental cause are associated by a failure of this invasion so that the placenta doesn't develop properly and therefore there's reduced utero placental blood. . So when we look at the blood flow, we know there's an association between abnormal blood flow or high resistance.

With inadequate trophoblast invasion, we can use this raised resistance in the uterine artery Doppler at 20 weeks to predict a higher chance of having a growth restricted baby. So we use this measurement at the 20 week [00:15:00] scan to help us determine which babies we should be scanning more frequently in the third trimester to look for growth problems.

If you look carefully at the guideline from the RCOG about growth, restriction. You'll see that the evidence for uterine artery dopplers demonstrates definite value in high risk populations. These are groups of women that have a higher chance of having a growth restricted baby, such as women with blood pressure problems, women who smoke or perhaps are older.

So in these women performing the uterine artery Doppler can be helpful. It's a screening test. It's less obvious why in some places, including my own unit, we're using this screening [00:16:00] test for everybody because there's less evidence that this is of benefit in a low risk population. Remember, I've talked before about screening tests.

Part of the importance of a screening test is how prevalent the problem you're trying to detect is in the population so uterine artery screening ? Yes. Can be useful in some situations, yes. Can help us pinpoint which women we should be offering more scans to. But back to what we discussed in the Big Baby episode, we can cause increased anxiety and the same is true for some of the other screening tests that we use.

In pregnancy, introduced for one thing and then used for another. Pap A is another example. It's a serum screening test. [00:17:00] It's a placental factor initially introduced for down syndrome screening purposes, but because we are measuring it in many pregnant women, research has been done to see whether it and the other placental factors.

can have any predictive value of growth restriction in later pregnancy. PAPP-A is the only one that does a low PAPP-A, does have some predictive value for growth restriction at a later point in pregnancy. What do I mean by a low PAPP-A? A low level is less than 0.415. MoMs a MoM being multiple of the median i.e. your PAPP-A is [00:18:00] less than half of what it might be expected to be, and what's the increased risk if you have a low PAPP-A?

So the risk is around three times more than if you had a normal PAPP-A around three times more likely to have a baby less than the fifth centile, so the smallest 5%. So yes, some benefit of performing some extra scans, but far from definite that you're going to have a smaller or growth restricted. Why did I say dopplers can be muddling?

Well, up to now we've been talking about 20 weeks uterine artery dopplers. The dopplers we do later in pregnancy are umbilical artery [00:19:00] dopplers. But if we're careless and we use UAD as an abbreviation, we can be confused. And sometimes when women have their scan reports, they come and say to me, Well, my dopplers were abnormal at 20 weeks, but they're normal now because a well meaning midwife or sonographer has told them at 28 or 36 weeks the growth of your baby's normal, 

the water around baby is normal and the dopplers are normal. But what they're not telling and explaining to women is that the dopplers are completely different thing. So here we are measuring the blood flow in the umbilical artery that's in the umbilical cord. This is blood flow directly related to the baby's circulation.

We are looking for increased resistance [00:20:00] or in some very growth restricted babies. , there may be what we call absent or reversed and diastolic flow. These measures are important because they help to tell us when a baby should be delivered if growth restriction is detected. If growth problems are detected early in pregnancy, it's a balance between growth and maturity.

If a baby's small, the growth has significantly slowed. But the baby is preterm, then there's much more value of that baby staying in the womb and maturing, even if it's struggling to grow. Whereas closer to the due date, there's a much lower threshold for intervening. If a baby's very small at that stage, there's limited benefit to staying in the womb, and it can be much better for the baby to be born and start growing on the outside.[00:21:00] 

When a baby's small, it can be a very anxious time for prospective parents worrying and waiting between scans and clinic appointments. Sometimes the timing of things can seem arbitrary or confusing. We're saying we are worried about a baby because it's small. It's growth isn't good, and yet we're saying bye.

We'll see you in two weeks. The reason for this is the frequency of scans will depend on what we are looking at. If we are looking at growth measurements, then the measurements ideally need to be two weeks apart for any meaningful change. If we measure a baby repeatedly, sooner, closer together, then we won't be able to assess correctly whether it is actually growing.

Likewise, umbilical artery dopplers. . One of the best ways to monitor small babies [00:22:00] is if the umbilical artery Doppler is normal, then it's safe for us to repeat it in 14 days. There's no need to do any other tests. In the meantime, it's highly predictive that this baby is going to be okay for the next two weeks.

If, however, the umbilical artery Doppler is raised. And there's a need to continue the pregnancy because we're waiting for the baby to mature. Then monitoring and measuring twice a week is necessary because umbilical Artery Doppler does have a direct correlation with improved perinatal outcomes. So we want to know exactly what that resistance is and when it might move to absent or reversed end diastolic.

Remember I said that the baby can [00:23:00] redistribute things, sending more blood flow to its brain. So if we have an abnormal umbilical artery Doppler, we can look at the middle cerebral artery. That's the artery in the middle of the baby's brain. So here, rather than increasing when there's a. , the resistance to the blood flow is reduced.

It isn't actually a great predictor in preterm babies, but in small babies, at full term it can be. If the middle cerebral artery is abnormal, we might need to deliver that baby. The final sort of doppler that can be used is the ductus venosus the ductus, venosus represents the atrial. That's the smaller chamber of the heart.

Pressure volume changes during the cardiac cycle [00:24:00] as the baby's struggling and growth restriction worsens the blood flow velocity in the ductus venosus reduces. So this tells us a bit about the baby's heart function for small preterm babies. Monitoring the ductus venosus one of the best predictors of when we should deliver a baby.

If the ductus venosus Doppler becomes abnormal, then delivery is necessary. But like I said at the beginning, this wouldn't be done by me. This would be done by one of my fetal medicine colleagues. Alongside these dopplers for a small baby, we may also perform a computerized CTG or heartbeat monitor.[00:25:00] 

Remember, in one of the episodes on fetal heart monitoring, I talked about doors, Redmond criteria, and actually doors, Redmond criteria or computerized ctg. It can be crucial in deciding when to deliver a baby that's growth restricted Conventional CTG cardiograph has a big difference in intra and inter observer variability, but with computerized ctg, the fetal heart rate variation is the most useful predictor of fetal wellbeing

so we need to look at short term variation or S T V, and if this is less than three, there's a much higher rate of the baby not surviving, and [00:26:00] therefore much more urgency that this baby needs to be born now. So for a small baby, We'll use a combination of growth scans looking at two points in time, at least two weeks apart, umbilical artery, again, if it's normal, two weeks apart.

If it's abnormal, we'll look, if you're preterm at particularly the ductus venosus and the short term variation on the ctg. And if you're nearer term will be looking more at the middle cerebral artery. And in all these situations, we'll also be looking at the liquor volume or amniotic fluid, not forgetting the fact that we'll be asking you, is your baby moving?

[00:27:00] Because fetal movements or baby being active, baby moving around is a really good indicator that that baby is well. So you have a small baby, you'll probably be given some additional scans. More frequent appointments will also be looking for blood pressure issues because where there's a placental problem, often a smaller baby goes along with blood pressure problems, and then we'll be talking to you about perhaps having your baby a little bit earlier than you might have expected.

Birth will depend on just how small your baby is, as well as what stage of pregnancy you need to have your baby if you're very preterm and the baby's very small we'll usually be recommending a cesarean to put the least amount of stress on the [00:28:00] baby, and also because your body just simply isn't ready for labor.

If you're closer to your due date, then with a small baby, we may still try an induction. We'll explain to you that there's a higher chance of your baby getting stressed during labor. We'll recommend continuous heartbeat monitoring. During that process, but actually some small babies cope very, very well and very resilient and actually seem not to be troubled by labor at all.

But we will discuss with you that there's a higher chance of potentially needing an emergency caesarean if your baby becomes stressed. We'll also talk about different methods of induction of labor. Some of the prostaglandin hormone pessaries we might use may be more likely to cause stress in a smaller baby, and [00:29:00] therefore will often use more mechanical methods.

Something that softens and opens the cervix mechanically than hormone pess Aries, because there's less likelihood of stressing the baby with excessive contractions. So I'm hoping that that's given you a little bit of an overview of what to think about if we think your baby might be small. What's my zesty bit?

I think the most important aspect of today's episode is if we say your baby's a little bit smaller than average. Don't panic. There's lots we can do and it means that we've picked it. We've noted that your baby is a bit smaller and we're going to adjust the appointments, the scans, and even possibly the birth that we suggest for you accordingly.

Don't be [00:30:00] frightened to ask questions and understand what is happening to you. I've put some information in the program notes that might help answer a few of your questions. If you're currently. And you've been told you've got a smaller baby. If you're a professional listening to this, I think my zesty bit has to be, don't confuse uterine artery dopplers with umbilical artery dopplers.

They're two completely different things, and again, I've put some things in the program notes so that if you are uncertain, you can go away and have a little bit of a read. In a bit more depth and understand a bit more about what we're talking about. I very much hope you found this episode of the obs Pod.

Interesting. If you have, it'd be fantastic if you could subscribe, [00:31:00] 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 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 episode interesting and want to explore the subject a little more deeply, don't forget to take a look at the program notes [00:32:00] where I've attached some links.

If you want to get in touch to suggest topics for future episodes, you can find. @TheObsPod on Twitter and Instagram, and you can email me theobspod@gmail.com thank you for listening.