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We heard you. Nine years of bring back the snack wrap and you've won. But maybe you should have asked for more. Say hello to the hot honey snack wrap. Now you've really won. Go to McDonald's and get it while you can. Whoa. What? Why are they so small? As Women's healthcare professionals, OB GYNs, whatever, our diagnostic tool of choice is ultrasound phenomenal. I mean, if you're an ER practitioner, you know, you love your CT scans. Not mad at you, but boy, you CT everybody. Well, we kind of sono everybody. It's what we do. And the reason is, is that ultrasound for pelvic anatomy and obstetrical surveys are great. They just work. Although there are times where we need more information and an MRI can be helpful. On the ob side, fetal MRIs are phenomenal for intracranial structures or defects of the body and or spine. But without a doubt, ultrasound is the way to go. We're very comfortable with that as women's healthcare providers. But because we do so much ultrasound, sometimes we see things that are a little off. And we should note that because. But we should also know the diagnostic rules that apply to that. For example, fetal microcephaly. Now, I get it. We don't typically see that all too often. And the reason is, is based on who you read. It's about 2 or 10 in about 10,000 births here in the U.S. okay? Even though it varies across the world, it's about 2 or 10 per 10,000 births here in the US and obviously it's found by ultrasound. Now, we're going to cover this. We can't figure it out. We're going to talk about fetal microcephaly because just recently in our group, we had an ultrasound that was read with a head circumference of 4% with the tag, hey, this is concerning for microcephaly. So I kind of pumped the brakes there a little bit, said, well, is it though? Is it? You see, we are very used to using percentages for ultrasound and fetal weights and fetal biometrics. That's what we do, and we should do that. While fetal growth restriction is defined as an estimated fetal weight under 10% or an abdominal circumference under the 10th percentile, fetal microcephaly is a little different because while 4% actually sounds pretty concerning, I mean, it's way under a 10 percentile. But is that really fetal microcephaly? Now, the reason I pumped the brakes a little bit is because we don't really use at all percentages for that diagnosis. Guys, I know I'm getting ahead of myself. I was supposed to do this after the intro, but I can't help it. So here's where we're going. The proper diagnosis of fetal microcephaly actually isn't the percent from the mean for the head circumference. It's actually a standard deviation. So this is one of the weird times in obstetrics, guys, where you've got to look at the graph, right? So perinatology doctor, if you just put in perinatology.com head circumference, you get the beautiful little table with the mean of what the head circumference is as a mean. In other words, a 50th percentile based on gestational age. And then it has the second, third, and the fifth standard deviation below that. That is what matters. You see, a head Circumference can be 4%, which is obviously off the mean, but it may not necessarily meet criteria for fetal microcephaly. So let me just say right here, fetal microcephaly is not diagnosed by a percentage, but by a standard deviation from the mean. And I'm going to tell you what that standard deviation is as soon as we come back from the intro. It's a very easy little table. You literally go across the x axis by weights and on the Y axis is the millimeters and you just plot it. Very, very simple. So I'm gonna tell you what's the actual standard deviation that diagnoses fetal microcephaly. And then we're going to talk about some potential causes. What should we look for for this and what are the next steps here? Do we need a fetal mri? Is this something that we just go, hey, baby's head's kind of small? It is what it is. What do we do with this? So that's why I've decided to call this understanding fetal microcephaly. We actually touched on this a little bit very early on in our podcast origins, because 2016 or 2017, when Zika, remember that arbor virus, Zika, mainly in Latin American countries, was an insect borne virus primarily that caused fetal microcephaly. And it was devastating, even though there was very limited cases in the U.S. but because the population is very mobile, it caused a big concern. So we'll touch on that along with other causes of fetal microcephaly and the blood tests that we can consider to get here, as well as possible environmental exposures that mom have been exposed to to lead to this condition. But fetal microcephaly, guys, is something that we should not take for granted or just discarded as well. It's just a little small. No, no, no. Fetal microcephaly True. Fetal microcephaly diagnosed by the criteria of standard deviation is a big deal. It's linked to some poor neurocognitive issues and potentially some altered intracranial structures. That's why we have to talk about the workup. I think I've set it up enough. Let's get into Understanding Feedback Fetal Microcephaly coming up next. This episode is brought to you by Indeed. Stop waiting around for the perfect candidate. Instead, use Indeed Sponsored Jobs to find the right people with the right skills fast. It's a simple way to make sure your listing is the first candidate. C According to Indeed data, Sponsored jobs have four times more applicants than non sponsored jobs. So go build your dream team today with Indeed. Get a $75 sponsored job credit@ Indeed.com podcast. Terms and conditions apply. The world moves fast. Your workday even faster. Pitching products, drafting reports, analyzing data. Microsoft 365 Copilot is your AI assistant for work built into Word, Excel, PowerPoint, and other Microsoft 365 apps you use, helping you quickly write, analyze, create, and summarize so you can cut through clutter and clear a path to your best work. Learn more@Microsoft.com M365 copilot. This is Dr. Chapa's obgyn no spin podcast. They make your head seem smaller. Well, just like baby weights come in different sizes sometimes it's okay. So do baby heads, and they're not all microcephalic. So it's interesting, that ultrasound that I mentioned in our intro, you know, I was kind of doing a chart check as residents were seeing people, and I saw that, okay, I addressed that. And then I saw that same patient later on that afternoon. And oddly enough, and she had her faculties with her. She was, you know, she had normal mentation as far as I can tell, but she was very small, like under 5ft tall. She was from a South American country, and. And her head was pretty darn small. So I looked at her husband. I said, I'm, you know, not trying to be mean or anything, but does her head seem a little small to you? And she said, yeah, that, you know, the whole family kind of has a small head. And she said, yes, we kind of have small heads. I'm like, okay, hey, you. Do you. My point is, is that that's why percentages aren't used for head circumference. For the diagnosis of fetal microcephaly we use standard deviations because it's a little bit more forgiving, I guess you can say, because this is a big diagnosis and we got to get it right and we don't want to over call already, guys, already. The accuracy of fetal microcephaly based on standard deviation at the standard definition, which is three standard deviations below the mean. Everybody get that? Not percentage. Three standard deviations below the mean. And if you're thinking, wait a minute, man, our ultrasound machine uses percentages and a Hadlock. I get it, so does mine, so does the majority of people's. That's why you've got to go to the table and look per gestational weeks, look at the millimeters of head circumference. So if it's in centimeters, just move the decimal. Convert that to millimeters and look at the head circumference standard deviation. The definition of microcephaly according to SMFM is three standard deviations or more below the mean. Now, if it's two standard deviations, don't ignore that. I mean, it's pretty significant, but it doesn't meet the definition of microcephaly. You say, hey, the head Circumference is at 2 standard deviations below the mean. I'm still going to do the workup, which I'm about to tell you, and we're still going to trend, which is what you should do to make sure it doesn't become three standard deviations below the mean. Now, here's a quick thing, guys, for diagnosis very quickly, here's a clinical pearl right at the start. While fetal microcephaly is conventionally defined as a head circumference greater than 3 standard deviations SDs below the mean for gestational age, kind of the synchinon. In other words, the without doubt diagnosis is that if you get to a standard deviation of 5 1, 2, 3, 4, 5 below the mean, that's pretty darn pathological. All right, so we have like microcephaly, like kind of a small head, I'm concerned. But if you have one that's five standard deviation below the mean, which is on the table, that's pretty significant. That's probably not constitutional. That's probably not just familial. There's something going on there and that's linked to higher intracranial abnormalities. Those absolutely need a fetal MRI and detailed patient counseling because something is wrong there. Now, let me get into this very quickly because I don't want this to be belabored. We're going to do this very Quickly as things to know, things to look out for. We can talk about causes, workup and then be done. So the first clinical pearl is head circumference percentages. While those are significant, we don't use that to define microcephaly. We use standard deviations. That's first clinical pearl. Now, anybody, for me, who has a head circumference under the 10th percentile, it is fair, it's reasonable to look at the table because it's kind of small and place it on the graph and go, hey, well, the head circumference is 9% at this gestational age. According to headlock, it is not yet two standard deviations below the mean. So I'm way clear. As long as it's not, you know, three standard deviations or more. Does that make sense? So note it, but relate it. Head circumference has to be related to standard deviation for it to be smaller. All right, so just something to note, also, the positive predictive value. Guys, this is very well published out of perinatology. The positive predictive value is good, but it's not real good based on who you read. In general, the accuracy of fetal microcephaly, being diagnosed with a standard deviation of 3 below the mean, which is small when the child is actually born. And you plot that head circumference at birth as a neonatal or as a baby graph, there's a correspondence anywhere from 43 to 67%. So it's not bad, but it's not like 90%. So if we can split the difference, say it's about a 50% chance of being accurate, even though this red based on who you read is about 43 to 67% of having a positive predictive value at birth. However, here it is, guys. If you have a standard deviation of 5 below the mean, that's pretty damn good. I mean, that's pretty darn accurate. That's a small head, and you got to worry about that. There's other findings on ultrasound that raise the risk of concern. Obviously, if the frontal bones have abnormal scalloping or sloping of the forehead, that that implies absence of intracranial structures, that's a big deal. So as I mentioned to our resident when we reviewed this ultrasound, it's not just the percentage you want to take a look at, the images you want to look to see. Is there anything grossly off with the shape of those of that skull? Is it a weird lemon sign? Is it a sloping issue? And look at the intracranial structures, at least at the ventricles make sure there's no big, you know, holoprosencephaly or something else going on. So pay ATT attention to it. I look anything under 10%, that. That does get my attention. But that doesn't necessarily translate into microcephaly, because as we've already discussed, that's a standard deviation of 3 or below, with 5 being pretty darn concerning for a pathogenic cause there. All right? And that's devastating diagnosis. So how do you diagnose fetal microcephaly with ultrasound? Number one, two, not based on a percentage, but based on a standard deviation. And then number three, there's other factors that increase its positive predic value, like shape of the skull as well as anatomy of intracranial structures. Okay, so, oh, here's a weird little quinky dink. Am I gonna do this? Let me say this. So don't be mad. I'm telling guys, I'm telling you. Facts, right? This is not. This is not stereotype. I'm not being misogynistic. Whatever. I get plenty of those comments, thank you very much online, which I'm not. But people don't like what you say, and then they label you weird. Stu. Whatever. Bring it, baby, bring it. But in general, here's a little quinky dink. If somebody asks you who has bigger heads in utero, boys or girls? Because you got to pick one, boy or girl. In general, female fetuses generally have smaller head circumferences at a certain gestational age than males. Now, guys, when I was at Parkland, let me just give you this. One of the founders of Parkland ultrasound, who's now passed away, God rest his soul, he was very kind to me, Rigoberto Santos Ramos. He was Guatemalan. He was rock star. I mean, one of the. The true mental thankful man. I mean, I was brought up and trained under the shadows of these dinosaurs. These. And I mean that in a good way, these pillars of mfm. Anyway, he always said, ah, that's because babies have male ba. Male. Males have more air in their head. Females need less space to be smarter. Brilliant. Very, very nice recovery there. But, yes, female fetuses generally have a smaller head circumference compared to male fetuses for GE age, although that. I'm not implying that they have microcephaly. I'm just saying they tend to have a little smaller head by percentages compared to a male. So one of the things that you can consider like, oh, the head Circumference is, you know, 10, maybe 11% or so or 12% compared to the other variables is take a look at the little genitalia or look at the non invasive prenatal test. And if it's a female, go, Ah, got it. Understood. That's a normal finding. All right. Now some of those tend to narrow, the differences tend to decrease as you advance to term. But in general, the differences are most pronounced in the second trimester around the time of fetal survey. Right. So just a little quinky dink, if you're ever asked who has smaller head sizes in utero. Well, in a certain slice of gestation, which is around 18 to 22 weeks, females per gestational age will have slightly smaller head circumferences compared to males. But I'm not implying, of course, that those are microcephalic. These are still generally like in the 10 to the 20th percentile, whereas males may be maybe 20th to 25 percentile. So it's a little bit smaller. All right, just as a weird point, I don't know why that was necessary. I just found it interesting. You gonna leave that in there? Leave that in there. Well, that's good, man. Leave that in there. All right, so what the hell? What am I doing now? Yes, head circumference. So head circumference and standard deviation is key here. So if you have SD greater than 3, that's a big deal. Now, others have proposed to get us more comfortable with ratio and percentages, because that's what we do in obgyn. We like our percentages. Some people have published the head circumference HC to abdominal circumference, the ac to try to increase a positive predictive value for fetal microcephaly. Does that make sense? So small head compared to the body HC compared to abdominal circumference with a percentage around 3%. The problem is that that typically pans out to like two standard deviations below the NORMA normal mean. So that' sit's got great sensitivity, but it's terrible specificity because it tends to over call microcephaly. So just FYI, if you want to look at a percentage, you can head circumference over abdominal circumference. If that ratio is less than third percentile, it's a small head. I'm just call it what it is, man, small. But that may not necessarily be diagnostic of microcephaly because you gotta look at the table. All right, there is an 8C to abdominal circumference. By the way, that's also been looked at at term to try to predict shoulder dystoci. That doesn't work because it's not a big fat baby tummy that gets stuck. It's the shoulders and even head to biochromatal diameters. A lot of these calculators have been looked at. I did a peer review for one like ten years ago. Dude, the accuracy sucked. It was horrible. It over called crap and it scared people. So as of right now, we don't use those kind of ratios. Okay. Even the flac, femur lengths to abdominal circumference, I trained with a flac ratio, you know, less than 24% or so was one kind of growth restriction versus yeah, we don't do any of that anymore because they're just highly inaccurate and nonspecific. So short answers, how do we define fetal microcephaly? We define it based on standard deviation. All right, fine. Possible causes here, possible causes. Let's start with genetic stuff, which is what everybody worries about and we should. But in general, chromosomal abnormalities are pretty rare in terms of of issues like 13, 18 and 21. But it is important of course to have nips testing. So non invasive prenatal test is a big deal because if it's going to have a trisomy, it's going to be typically 13 or 18. All right, so 13, 18, 21. That's not very usual. But of course the first box easy to check off is it was the nips test done. And if it wasn't done, consider it because it's going to look for the main causes here, which is 13 or 18 if it is a chromosomal issue, but that's a chromosomal issue, mainly a trisomy. There are other possible causes that are more common as genetic conditions. Okay. Now most of these are single gene issues that are either autosomal, recessive or X linked issues like Smith Lemmel Opitz syndrome or Shekel syndrome, Meckel Gruber syndrome. These are weird stuff. I get it. So if you really are concerned about microcephaly and I do this eval, I call for a geneticist at a standard deviation of two or more just because I don't want to miss it. And I know it's not three, but I'm just, hey, let's take a look at something. We're kind of concerned here. Let's just get ahead of it, make sure we've got nips and we do serial trend because two standard deviations is small, even though it doesn't meet the diagnostic criteria. I don't want to ignore that. All right, so bring in genetics. It's a nice thing to evaluate or look for. Sometimes non invasive prenatal tests can do SNP evaluations for some autosomal, recessive or X linked patterns of inheritance. Okay, so first that was genetics. Other potential causes, of course, are infections. So, Torch, you know I hate tort serologies. You know, you've heard me say that before, because they are horribly difficult to read and they take acute and convalescent serum. Unless you look at the avidity of the antibody response specifically for igg. And I've covered this in the past, I'm not going to get into it now. But if you're going to do torch, remember the best way to figure out if somebody has a TORCH infection, which microcephaly can be, can be a result of. You should really tap the fluid and send that for pcr. That's the best. But if you're going to do serologies, if they're all negative, that's phenomenal. But you got to check it again to make sure that there's no level increase in the antibody which could signify an acute flare. You'd figure they would be IgM positive already because if the child is having manifestations, but nonetheless, if you can catch it in a window, the astrology may be negative. You got to check it again and remember that talk. So because IGG picks up pretty quick and lasts forever, you got to look at the avidity, not affinity. The avidity A V, I, D, I, T Y the avidity of the antibody, because lower avidity means more acute infections, higher avidity means that they've been there a while. So you've got to look at a specific antibody type. What's their flavor? How old is the antibody for acute or chronic infection? Although these TORCH infections typically would have other manifestations in the child, like intracranial lesions, maybe some calcifications in the eyes. So you'd find other issues. It would be rare to just have isolated microcephaly from torch, but again, check the box. All right, so do a thorough history. Are you around weird cats? Any weird rashes? Look for things. And it's reasonable to look for tort serologies, knowing, of course, you got to know how to interpret those. Okay, so IGM is always best, but sometimes those are variable. IGG is hard to read unless you include an avidity. Or do acute and then check it later in two to three weeks to see if there's a change in antibody titer. Just for historical reference, we mentioned that I think in the Intro. Zika was an Arborvorne virus. It's still out there. It's just. It's slightly decreased now because there's insecticides and pesticides that have really taken care of the vector. But the Zika virus was a big cause of microcephaly. Not that big of a deal anymore. Although if you do have a very transient patient population, as we do, and you find true fetal microcephaly, say, where have you been? I mean, have you been in the jungles of Ecuador or Honduras? Zika may be a thing. And there's specific tests for Zika that you can order either through your health department or through the cdc. Whoa. What? Why are they so small? Now, outside of genetics, outside of potential infections like Torch and. Or Zika, there's some substances that mom could be exposed to that can lead to this. I mean, severe cigarette smoke can lead to microcephaly, alcohol. Of course, small heads are part of fetal alcohol syndrome and even metabolic issues. Guys, here's a weird step question. If you're in med school or, I guess, getting ready to take step three or whatever, or in training, this is a nice review of faculty. Here's how you totally would stump somebody, because few people remember this. Give me a metabolic condition in the mother that can present with fetal microcephaly. Give me a metabolic condition in the mama that if she's not taking care of herself and it's not diabetes, can give you isolated microcephaly. Anyone? Anyone actually is a big cause of it. If a patient with phenylketonuria does not follow her specific diet. Guys. Because they need to remember that they need a specific type of diet so that their blood phenylaline levels don't rise. But if they do get too high, it is a CNS teratogenic. Guys. So maternal metabolic abnormalities, specifically pku. If mom has PKU and she's not taking of herself by eating a low phenylalanine diet and she gets pregnant, that's bad. I mean, it's like, based on who you read? I quote patients 80 to 85%. That's what the literature says. Risk of microcephaly with this thing. I mean, it's legit. And those children are. Are very effective with learning disabilities, congenital heart defects. PKU needs to be respected. PKU needs to be respected in a childbearing woman, because, man, they gotta stick to that. All right, let's get ready to wrap this up very quickly. Fetal mri. EA or nay? The answer is yay. Yes. Fetal mri. Once you meet criteria And I don't mean the standard deviation of 1, 2. You know, I don't think that's necessary. But at 3 or more, it is kind of recommendation to get a fetal mri. Here's the catch, guys. One of the last clinical pros that we're gonna do. Even watch this, guys. Even with normal ultrasound findings. Now, why is that? Very easy. MRI detects more things than the ultrasound based on their level of cuts, slices. But here's the catch. The radiologist don't just send it to Joe Schmo. No, no offense. To Joe Schmo. To Joe Schmo, radiologist. It needs to be somebody at a fetal diagnostic center who knows how to do, ideally, a fetal neuroradiologist. Yeah, they're rare, but they are out there. They've got to know what they're looking at here. So fetal MRI is strongly recommended as an adjunct to ultrasound, especially in cases of isolated head circumference, even without any gross abnormalities on ultrasound. Say you're going to an MRI at a fetal diagnostic center, especially with three standard deviations or more. Two standard deviations, that's up to you. If you want to be complete phenomenal, I think that's fine. But remember, the diagnosis is three or more, and at five standard deviations below the mean. Absolutely. You definitely need to do that because there's things like encephalocele, holoprosencephaly that meant you got to know both for prognosis and for patient education and for planning, you got to know that. So fetal mri. Short answer is yes, if you need diagnostic criteria, but send it to a specialist. Do these babies need endopartum surveillance? Yeah, for sure. It's very reasonable because they've got a true CNS abnormality. And if the cns, if the brain is off, it could affect coordination of impulses to the heart. So, yes, you definitely could consider antepartum fetal surveillance. The guidelines are plus or minus on that for me, personally. I know it increases potential interventions, but this child has a true abnormality. And so, sure, antepartum fetal surveillance, weekly testing seems to be fine. Most guidance do address that. Some add Dopplers. I don't know if that necessarily has great data. The data is kind of unsure about that. But antepartum fetal surveillance, like BPPs or modifieds, is a great way to go. And of course, you need to continue doing serial ultrasound, not just to track the head circumference, but also to track fetal growth, because there could be altered fetal growth that that follows this diagnosis. All right? So if you find it, don't stop looking. If you find it, keep looking for a cause. If you find it, do surveillance both for growth and for endopartum fetal surveillance, because this is a big deal. This has poor prognosis if it's at 3 standard deviations below the mean and absolutely devastating at 5 standard deviations below the mean. Okay, so I think I've covered what I'm supposed to. The short of it is fetal microcephaly, we don't see it a lot. So I thought this was a good topic as a good reminder that percentages are a big deal, but it's not diagnostic of the condition unless we're talking about standard deviations. So remember, three is a cutoff. Five is really bad. And the last thing I want to give you, and I'll put this in our show notes, is the Society of Obstetrics Gynecology from Canada. SOGC has a wonderful review on this. It's their Committee opinion number 380380, which is titled Investigation and Management of prenatally identified microcephaly 2019 stellar. Which is really good. And I know it's been a couple of years, 2019, but nothing really has changed in there. It's very detailed, it's very nicely done. Also, the Fetal Medicine foundation has nice information on microcephaly. A little bit more patient friendly if you need to give some patient information. Podcast family, I think we have wrapped up understanding fetal microcephaly. As always, we're thankful for you. We're glad you're part of our podcast family. Now that we've done all that, let's take it home. Ready to relax in your dream bath retreat without the stress of figuring out every detail yourself at the Home Depot, your bath upgrade is covered shop fully designed rooms and curated bath collections to go from inspiration to transformation. Fast savings of up to 40% will make it easier on your budget and find everything you need from tubs to toilets and all the tile in between to bring your vision to life. The Home Depot Dream Baths built here. This has been Dr. Chapa Zobetyn, no Spin Podcast podcast family. Thank you for your support. Thank you for listening and as always, we'll see you on another episode of the no Spin Podcast.