Understanding First Trimester Ultrasound

Hi everyone, my name is Ajit Panag. I'm one of the emergency ultrasound fellows if you haven't met me yet. Today we're going to be talking about first trimester pregnancy ultrasound and we'll be going over a bit of a review of indications, some anatomy review, and then we'll talk about prototype, some of the technique, and some of the pathology involved. So first of all, what are some of the indications for first trimester ultrasound? Are you just going to ultrasound everybody who's in their first trimester? Probably not. But if you have a positive pregnancy test and any one of these type of symptoms or signs or complaints, then I think it's a good idea to go ahead and try that ultrasound. Pelvic pain, any abdominal pain, vaginal bleeding, any sort of dizziness or syncope and any sort of pelvic mass. So the big kind of key clinical questions that we're trying to answer with this are. Is there an intrauterine pregnancy or is it maybe an ectopic pregnancy? Is there pregnancy loss or is there a viable pregnancy? And we'll talk about some ways we can assess viability. As well, are there any other findings? So maybe MULTIPS or maybe some gestational tracheoblastic disease or other things that we can pick up along the way. But really, first and foremost, we need to make sure that this pregnancy is in the right place. So we'll talk about a few definitions before we get started. One of those is gestational age. So this is generally measured from the first day of the last menstrual period. And since ovulation is generally two weeks after the first day of the last menstrual period, you can consider this gestational age to be the age of conception plus two weeks. Next we'll just talk about this concept of this discriminatory zone. This comes up all the time on board exams, on the emergency medicine boards, and in-service exams, and others. So the serum HCG level above which a gestational sac should almost always be visualized on ultrasound when an intrauterine pregnancy is present is the kind of definition for this. And the numbers that the boards have used traditionally is around 12 to 1500 for transvaginal ultrasound and for transabdominal, usually around 5,000 to 6,000. However, some more recent literature has shown that depending on the operator, Transvaginal ultrasound could be somewhere between 1 to 2,000 and transabdominal somewhere between 3 and 5,000. So to review some anatomy, the uterus, it sits between the bladder anteriorly and recto sigmoid colon posteriorly. The most common position for this is going to be the anti-flexed uterus. And when it's anti-flexed, the uterus will create... a 90 degree angle with the vaginal canal. And we'll take kind of take a look at what this looks like in a minute. And then the fallopian tubes and the ovaries are going to be entering the uterus at the cornea, each cornea laterally. So here's kind of an image to help jog the memory. The uterus is kind of an inverted pear shape in the center, right in the midline of the true pelvis. And the uterine body and the fundus are actually intraperitoneal. So this is why if you have a ruptured ectopic pregnancy, you can see some positive intraperitoneal free fluid, which becomes important in just a little bit. The anterior cul-de-sac is between the bladder and the uterus. This is a potential space. And then the posterior cul-de-sac is the potential space between the uterus and the colon. So the anterior cul-de-sac is usually empty, but it can contain loops of bowel or free fluid. And the posterior cul-de-sac is also known as the pouch of Douglas. And it actually usually does contain some bowel loops. The posterior cul-de-sac is the more dependent portion in the supine patient. So look here for any pooling of free pelvic fluid. And here's kind of an image of what that looks like. You can see the bladder anteriorly in the sagittal cut here with the uterus just behind that. And then the recto sigmoid colon just behind that. And you can kind of... see this 90 degree angle we talked about with the uterus and going into the cervix and then the vaginal canal. So probe type, you can really do this with either probe. Today, we're going to be focusing on transabdominal ultrasound, which will be kind of best performed by the low frequency curvilinear probe. This kind of gives us a bigger picture of what's going on with the uterus and the anexa kind of all in one. Whereas you can get a a more detailed image with the transvaginal probe or endocavitary probe. And it has been shown that POCUS can also be done pretty quickly and effectively by emergency physicians with transvaginal probes. And certain centers do perform this regularly, but it is much less common, much less frequent. So the technique and positioning for the patient, you're going to want your patients supine so that if there is any sort of cooling of intraperitoneal fluid, you'll be able to catch it. And you'll want a full bladder. And this is, again, for the transabdominal ultrasound. For the transvaginal, you'll actually want a empty bladder, but we'll just be focusing on the transabdominal. So you're in the ED. Are you really going to give your patient a glass of water and then wait an hour like they would in the outpatient OB world? It's not really practical, so just scan when you can. Alternatively, if your patient needs an IV or blood draw regardless and is stable, you can infuse IV fluids rapidly and then take a look. It should fill up the bladder much more rapidly than PO fluids would. This is important because of course transabdominally, you're going to be using the bladder as your window, your acoustic window to get much better resolution of what's behind it. And so this is a picture from the POCUS 101 website showing kind of the supine patient and the first positioning of the probe. You'll notice that the probe is in the sagittal orientation and in the midline, directly in the midline, just superior to the pubic bone. So this is the kind of traditional first view that you'll get, the midline sagittal view, as I just said. place your transducer on the midline abdominal wall, just above the pubic bone indicator to the head or cephalad. And you should be able to see the longitudinal uterus with the midline stripe visible. We'll see it in just a second. And then we'll talk about, and then we'll see the cervix that's just posterior to that angle of the bladder. And then you'll actually see the vaginal stripe to the right of the screen or more caudal. So here's an image of what that looks like. So anterior is at the top of the screen, posterior at the bottom of the screen, superior, of course, where the indicator is towards the head, and then the feet are down here. You see the bladder and the fundus of the uterus with this endometrial stripe going into the cervix, into this 90 degree, turning into the vaginal stripe. There's a bit clearer image of that. So again, you can see with a full bladder how much clearer that resolution is. And just back here is that pouch of Douglas. So one kind of pitfall when looking for free fluid is that the depth is not set high enough, actually. I know we're always telling everyone to reduce the depth to get better detail, but frequently, especially on FAST exams and OB exams, we need to see the back of the uterus and just what's behind it to really evaluate fully for intraperitoneal fluid. Okay, and here's a clip of that. So again, you can kind of see the bladder here, the uterus here, and you can see that nice 90 degree angle. Here's, I think, the same image just colorized to show the uterus and the bladder kind of nicely. I'll play that clip one more time. Okay, the second view on the transabdominal protocol is to get the midline transverse view. So you're just going to turn your probe 90 degrees. towards the, counterclockwise towards the patient's right and the indicator to the patient's right. And again, same thing right above the pubic bone. It is much lower than you think. So be sure to appropriately drape your patients. This view will show you the transverse uterus in sections from the cervix, and then you can kind of fan all the way to the fundus. And sometimes if you kind of tilt your probe one way or the other, you can sometimes see the adnexa and the uterus in the same image. Although this does kind of depend on, you know, supportive anatomy and a full bladder definitely helps. And so this is your transverse midline view. You can kind of see the bladder at the top there. And then you see your uterus here. If you pay attention to the kind of end of this clip, there is some shadowing within the uterus. And I think that is an IUD. So going up towards the fundus here and there's the shadowing. So you may see that as well. Great. Okay. So moving on to your actual protocol. Now that we've reviewed some of the anatomy, what are these, what are we actually looking for and how do we use this with patients? So the kind of age old question, when you have a positive pregnancy test, with no formal ultrasound that's been done outpatient is you have to make sure it's in the right place. So intrauterine versus ectopic. So this has a decent amount of text on this slide and I apologize for that, but there are some very important definitions here. The first thing that you will see in the developing pregnancy and we'll go progressively through the timeline and all of the numbers, by the way, in the top right hand of the screen are going to be four weeks of the trans abdominal ultrasound. For transvaginal ultrasound, you'll see all of these findings about a week earlier, give or take. So the gestational sac and double decidual sign is going to be kind of the first thing you'll see on transabdominal. The gestational sac is a sonolucent center or the chorionic sac surrounded by a thick, symmetric and fairly echogenic ring. And you'll see why that becomes kind of important. An echogenic ring, which is known as a chorionic rim. And next, you'll see a double decidual sign, which is two concentric echogenic rings surrounding a gestational sac. The inner ring is known as the decidua capsularis and the outer ring is known as the decidua. parietalis. And this is only actually seen in about 50% of pregnancies. And very importantly, all of these make intrauterine pregnancy much more likely, but they're not diagnostic. So this is a pictograph of the double decidual sign. So you can kind of see this gestational sac in the center with the inner decidua and then the outer decidua within the endometrial cavity. This is what it looks like on Sono. See this very bright kind of echogenic ring around the gestational sac and then the two decidua around that. And then this is just a gestational sac. Okay, the reason we need to be aware of this finding, even though it's not diagnostic of an IUP, is because there is this thing that exists called a pseudogestational sac. which is the idea that a small collection of intrauterine fluid can actually be erroneously mistaken for a true gestational sac. This can be present in ectopic pregnancies and so how you differentiate this from a gestational sac is that it's usually going to be more irregularly shaped and not kind of a perfect circle like this. It's going to have sharp edges kind of like we're used to seeing intraperitoneal fluid. We're used to describing it as having kind of sharp edges. This is intrauterine, but same idea. The border is not as echogenic. And so the gestational sac is going to have that nice bright border around it. The pseudogestational sac is not completely anechoic in its fluid in the center. So there's going to be some echoes and there's not going to be any contents inside. So there's not going to be any yolk sac or embryo or anything else. And this is kind of the the pseudo gestational sac when it looks like in cartoon and what it looks like on a real sonographic image. So you can kind of make out those sharp borders. Note that there's some echoes inside here and it's not completely black on the inside. And notice that you can't really tell the rest of the uterus from the border of this pseudo gestational sac. So there's not a really bright border around it. OK, moving on. the yolk sac. So this is going to be your actual first definitive evidence of an intrauterine pregnancy. It's going to be a circular echogenic ring with an anechoic center seen eccentrically, meaning not exactly in the center, kind of off to the side a little bit in the gestational sac. It actually helps transfer some nutrients to the embryo during the first trimester. And some early hematopoiesis actually also happens in the yolk sac. It will shrink and disappear by 12 weeks, but most of your patients that you're kind of deciding whether or not there's a IUP or an ectopic are going to be in that 5, 6, 7, 8 week range. So hopefully you will see a yolk sac before it disappears. And once it's disappeared, there'll be many other things to prove that it's an IUP. This is a picture of a yolk sac. So you can kind of see that gestational sac with that hyper-echoic or echogenic, I should say, rim. and the yolk sac within it kind of off to the side, not right in the center. So if you see this, you're good. You can stop unless there's a history of in vitro fertilization, IVF, fertility treatments, things like that. And we'll talk about that. So the kind of next thing you'll see is fetal pole and embryo and transabdominal ultrasound. You should start to see this by around six to seven weeks. A fetal pole is defined as a thickening or small mass at the margin of the yolk pack but by seven weeks it becomes not just a small mass at the margin but it actually becomes its own distinct structure. but it starts off as just kind of this bud off of the yolk sac. If you see this, also great, this is definitive evidence of an IUP. So you can kind of see this is probably more of a six-week embryo, whereas once it starts to grow a little bit more, it becomes a little bit more of its own distinct entity off of the yolk sac and known more as a fetal pole at this point. Cool, okay. fetal cardiac activity. So we've covered before, and you may have heard in some introductory ultrasound lectures about the ALARA principle, that is as low as reasonably achievable. So the idea is that Doppler, when you use Doppler with ultrasound, you have much higher energy levels than when you use just B-mode or M-mode. And so... fetuses and embryos are particularly susceptible to potential harm from Doppler, from energy, which is why M-MODUS preferred over pulse wave Doppler. And so how you'll measure fetal cardiac activity, and we'll take a look at a couple of clips after this, but to kind of go through the steps first, you'll locate the fetal heart and it should be kind of this little beating thing within the fetal pole and optimize your depth. So if you can get a view where the fetus is kind of more anterior, that's preferable. Kind of reduce your depth as much as possible. And then there's actually a zoom function you can use on most of the ultrasound machines. And zooming in on the fetus will also kind of help you get your M-mode cursor right over the heart and get a more accurate reading. Then you'll place your cursor over the heart and activate M-mode. Then you'll use the calculation package on your machine to kind of place two vertical cursors at each heartbeat and the machine should give you a fetal heart rate. So to kind of demonstrate that here's a fetus and if you can kind of take a look there is this small beating heart here and so what you do is you would place your cursor right over where you think the the heart is and you should be able to see a repeating pattern about the same depth as the the fetal heart. And so if you look on this bottom image, you can kind of see this, I'm kind of outlining it with my mouse here, this heartbeat and another one here and another one here. You want your vertical cursors to be at the same place on each heartbeat. So either at the start or at the end is usually preferable. Sometimes if you're too close to the machine, it's difficult to make out the actual heartbeats, taking a step back. will usually help differentiate this. These are your normal fetal heart rates for gestational age. So around six to seven weeks is when you'll first be able to start seeing it on transabdominal. So that's why I haven't listed anything prior to this. But your fetal heart rate will be around 100 to 120, and then eight weeks, 140s to 170s, and then 120 to 160 is kind of the normal fetal heart rate after nine weeks. Okay. ectopic pregnancy. So the idea with ruling in intrauterine pregnancy is that it's much, much easier to rule in an intrauterine pregnancy than to find hard evidence of an ectopic because with transabdominal ultrasound, which is what the majority of emergency departments are using, the adnexa are just so hard to evaluate. Even with transvaginal ultrasound, it's much easier to rule in an IUP than to rule in an ectopic. However, in saying that, there are some features. and some signs that you can use to help identify a ectopic pregnancy. The majority are going to be found in the fallopian tube and the ampullary region of the fallopian tube, but they can be found almost anywhere in the myometrium, in the abdomen, in the cornea, which is where the fallopian tubes meet the uterus, really anywhere. So if you Rulin and IUP don't try to find the ectopic unless, like I said, they're on in vitro fertilization or other fertility treatments that make something called a heterotopic pregnancy, which is the presence of an IUP plus an ectopic somewhere else, much more likely. So if you have a positive pregnancy test, then your uterus is empty. The next thing you would do in a stable patient would be to look for some of these signs. I would argue the first thing you should do is actually the third thing that's listed here. Look for intraperitoneal free fluid. um, hepatorenal space fluid is pretty highly sensitive for ectopic, but really any peritoneal free fluid should raise suspicion. You can look for something called a tubal ring sign, which is a thick hyperechoic ring around the tubal mass. This is the most specific for ectopic, 95%. And then there's something called the ring of fire sign, which is based around the idea that ectopic pregnancies have a high vascular region around them. And so you can look for high velocity flow on cholera Doppler surrounding them. This is the... tubal ring sign. So you can kind of see this this ectopic here with very thick echoes around it. Okay and then this is going to be your ring of fire sign. So this is a visualization of the right indexa and you can kind of see with color doppler that there's lots and lots of flow around here. This is not to be mistaken with a with a corpus gluteal cyst, which can have a similar appearance to a tubal ectopic. It can actually have a similar appearance to both a tubal ring sign and a ring of fire because both a corpus gluteal cyst is going to have lots of vascularity as well. And it's going to be kind of a ring in the, in and around the adnexa. So how you differentiate this is the corpus gluteal cyst is going to have less echoes. It's going to be a bit thinner. And the fluid inside is going to be clear and anechoic. And there's not going to be any stuff inside. So no yolk sac or fetal pole. And so this is a corpus luteal cyst. And you can kind of see there's more anechoic fluid inside. It's a bit thinner than that tubal ring that we saw earlier. This is much thicker. However, I should say that these kind of more specific signs for ectopic are things that you should look for in more stable patients, at least hemodynamically stable patients. Because if you have an empty uterus, a positive pregnancy test, even without looking for free fluid, I think that, you know, an unstable patient should be, you should be getting a surgical consult or an OB consult for that. With free fluid, an OB consult becomes much more, much more readily obtainable. but you should be calling right away. With a stable pregnancy, a stable patient rather, you can look for some of these things and they can help figure out what's going on. Okay, so some other kind of just a couple of things that can come up with first trimester pregnancy ultrasound. You can have a molar pregnancy and this is kind of that snowstorm appearance where um your HCG level is significantly elevated out of proportion and you don't see any sort of intrauterine fetus or embryo or anything else. This is obviously not viable and you would reach out with an OB consult to get this evacuated. And then just wanted to share a quick fun picture of twins. So you can kind of see this uterus with a couple little fetuses inside. And that's all I have. So some of the key takeaways are that you always need to be ruling in intrauterine pregnancy with any pregnant patient, especially if they are hemodynamically unstable, you need to be going to the ultrasound first and foremost.

Are you just going to ultrasound everybody who's in their first trimester? Probably not. But if you have a positive pregnancy test and any one of these type of symptoms or signs or complaints, then I think it's a good idea to go ahead and try that ultrasound.

Pelvic pain, any abdominal pain, vaginal bleeding, any sort of dizziness or syncope and any sort of pelvic mass. So the big kind of key clinical questions that we're trying to answer with this are. Is there an intrauterine pregnancy or is it maybe an ectopic pregnancy?

Is there pregnancy loss or is there a viable pregnancy? And we'll talk about some ways we can assess viability. As well, are there any other findings? So maybe MULTIPS or maybe some gestational tracheoblastic disease or other things that we can pick up along the way. But really, first and foremost, we need to make sure that this pregnancy is in the right place.

So we'll talk about a few definitions before we get started. One of those is gestational age. So this is generally measured from the first day of the last menstrual period. And since ovulation is generally two weeks after the first day of the last menstrual period, you can consider this gestational age to be the age of conception plus two weeks. Next we'll just talk about this concept of this discriminatory zone.

This comes up all the time on board exams, on the emergency medicine boards, and in-service exams, and others. So the serum HCG level above which a gestational sac should almost always be visualized on ultrasound when an intrauterine pregnancy is present is the kind of definition for this. And the numbers that the boards have used traditionally is around 12 to 1500 for transvaginal ultrasound and for transabdominal, usually around 5,000 to 6,000.

However, some more recent literature has shown that depending on the operator, Transvaginal ultrasound could be somewhere between 1 to 2,000 and transabdominal somewhere between 3 and 5,000. So to review some anatomy, the uterus, it sits between the bladder anteriorly and recto sigmoid colon posteriorly. The most common position for this is going to be the anti-flexed uterus.

And when it's anti-flexed, the uterus will create... a 90 degree angle with the vaginal canal. And we'll take kind of take a look at what this looks like in a minute. And then the fallopian tubes and the ovaries are going to be entering the uterus at the cornea, each cornea laterally. So here's kind of an image to help jog the memory.

The uterus is kind of an inverted pear shape in the center, right in the midline of the true pelvis. And the uterine body and the fundus are actually intraperitoneal. So this is why if you have a ruptured ectopic pregnancy, you can see some positive intraperitoneal free fluid, which becomes important in just a little bit. The anterior cul-de-sac is between the bladder and the uterus. This is a potential space.

And then the posterior cul-de-sac is the potential space between the uterus and the colon. So the anterior cul-de-sac is usually empty, but it can contain loops of bowel or free fluid. And the posterior cul-de-sac is also known as the pouch of Douglas.

And it actually usually does contain some bowel loops. The posterior cul-de-sac is the more dependent portion in the supine patient. So look here for any pooling of free pelvic fluid.

And here's kind of an image of what that looks like. You can see the bladder anteriorly in the sagittal cut here with the uterus just behind that. And then the recto sigmoid colon just behind that. And you can kind of... see this 90 degree angle we talked about with the uterus and going into the cervix and then the vaginal canal.

So probe type, you can really do this with either probe. Today, we're going to be focusing on transabdominal ultrasound, which will be kind of best performed by the low frequency curvilinear probe. This kind of gives us a bigger picture of what's going on with the uterus and the anexa kind of all in one.

Whereas you can get a a more detailed image with the transvaginal probe or endocavitary probe. And it has been shown that POCUS can also be done pretty quickly and effectively by emergency physicians with transvaginal probes. And certain centers do perform this regularly, but it is much less common, much less frequent. So the technique and positioning for the patient, you're going to want your patients supine so that if there is any sort of cooling of intraperitoneal fluid, you'll be able to catch it. And you'll want a full bladder.

And this is, again, for the transabdominal ultrasound. For the transvaginal, you'll actually want a empty bladder, but we'll just be focusing on the transabdominal. So you're in the ED.

Are you really going to give your patient a glass of water and then wait an hour like they would in the outpatient OB world? It's not really practical, so just scan when you can. Alternatively, if your patient needs an IV or blood draw regardless and is stable, you can infuse IV fluids rapidly and then take a look. It should fill up the bladder much more rapidly than PO fluids would. This is important because of course transabdominally, you're going to be using the bladder as your window, your acoustic window to get much better resolution of what's behind it.

And so this is a picture from the POCUS 101 website showing kind of the supine patient and the first positioning of the probe. You'll notice that the probe is in the sagittal orientation and in the midline, directly in the midline, just superior to the pubic bone. So this is the kind of traditional first view that you'll get, the midline sagittal view, as I just said.

place your transducer on the midline abdominal wall, just above the pubic bone indicator to the head or cephalad. And you should be able to see the longitudinal uterus with the midline stripe visible. We'll see it in just a second. And then we'll talk about, and then we'll see the cervix that's just posterior to that angle of the bladder. And then you'll actually see the vaginal stripe to the right of the screen or more caudal.

So here's an image of what that looks like. So anterior is at the top of the screen, posterior at the bottom of the screen, superior, of course, where the indicator is towards the head, and then the feet are down here. You see the bladder and the fundus of the uterus with this endometrial stripe going into the cervix, into this 90 degree, turning into the vaginal stripe. There's a bit clearer image of that. So again, you can see with a full bladder how much clearer that resolution is.

And just back here is that pouch of Douglas. So one kind of pitfall when looking for free fluid is that the depth is not set high enough, actually. I know we're always telling everyone to reduce the depth to get better detail, but frequently, especially on FAST exams and OB exams, we need to see the back of the uterus and just what's behind it to really evaluate fully for intraperitoneal fluid.

Okay, and here's a clip of that. So again, you can kind of see the bladder here, the uterus here, and you can see that nice 90 degree angle. Here's, I think, the same image just colorized to show the uterus and the bladder kind of nicely. I'll play that clip one more time. Okay, the second view on the transabdominal protocol is to get the midline transverse view.

So you're just going to turn your probe 90 degrees. towards the, counterclockwise towards the patient's right and the indicator to the patient's right. And again, same thing right above the pubic bone. It is much lower than you think. So be sure to appropriately drape your patients.

This view will show you the transverse uterus in sections from the cervix, and then you can kind of fan all the way to the fundus. And sometimes if you kind of tilt your probe one way or the other, you can sometimes see the adnexa and the uterus in the same image. Although this does kind of depend on, you know, supportive anatomy and a full bladder definitely helps. And so this is your transverse midline view.

You can kind of see the bladder at the top there. And then you see your uterus here. If you pay attention to the kind of end of this clip, there is some shadowing within the uterus.

And I think that is an IUD. So going up towards the fundus here and there's the shadowing. So you may see that as well. Great. Okay.

So moving on to your actual protocol. Now that we've reviewed some of the anatomy, what are these, what are we actually looking for and how do we use this with patients? So the kind of age old question, when you have a positive pregnancy test, with no formal ultrasound that's been done outpatient is you have to make sure it's in the right place. So intrauterine versus ectopic.

So this has a decent amount of text on this slide and I apologize for that, but there are some very important definitions here. The first thing that you will see in the developing pregnancy and we'll go progressively through the timeline and all of the numbers, by the way, in the top right hand of the screen are going to be four weeks of the trans abdominal ultrasound. For transvaginal ultrasound, you'll see all of these findings about a week earlier, give or take.

So the gestational sac and double decidual sign is going to be kind of the first thing you'll see on transabdominal. The gestational sac is a sonolucent center or the chorionic sac surrounded by a thick, symmetric and fairly echogenic ring. And you'll see why that becomes kind of important.

An echogenic ring, which is known as a chorionic rim. And next, you'll see a double decidual sign, which is two concentric echogenic rings surrounding a gestational sac. The inner ring is known as the decidua capsularis and the outer ring is known as the decidua.

parietalis. And this is only actually seen in about 50% of pregnancies. And very importantly, all of these make intrauterine pregnancy much more likely, but they're not diagnostic.

So this is a pictograph of the double decidual sign. So you can kind of see this gestational sac in the center with the inner decidua and then the outer decidua within the endometrial cavity. This is what it looks like on Sono.

See this very bright kind of echogenic ring around the gestational sac and then the two decidua around that. And then this is just a gestational sac. Okay, the reason we need to be aware of this finding, even though it's not diagnostic of an IUP, is because there is this thing that exists called a pseudogestational sac. which is the idea that a small collection of intrauterine fluid can actually be erroneously mistaken for a true gestational sac.

This can be present in ectopic pregnancies and so how you differentiate this from a gestational sac is that it's usually going to be more irregularly shaped and not kind of a perfect circle like this. It's going to have sharp edges kind of like we're used to seeing intraperitoneal fluid. We're used to describing it as having kind of sharp edges. This is intrauterine, but same idea.

The border is not as echogenic. And so the gestational sac is going to have that nice bright border around it. The pseudogestational sac is not completely anechoic in its fluid in the center.

So there's going to be some echoes and there's not going to be any contents inside. So there's not going to be any yolk sac or embryo or anything else. And this is kind of the the pseudo gestational sac when it looks like in cartoon and what it looks like on a real sonographic image.

So you can kind of make out those sharp borders. Note that there's some echoes inside here and it's not completely black on the inside. And notice that you can't really tell the rest of the uterus from the border of this pseudo gestational sac.

So there's not a really bright border around it. OK, moving on. the yolk sac. So this is going to be your actual first definitive evidence of an intrauterine pregnancy. It's going to be a circular echogenic ring with an anechoic center seen eccentrically, meaning not exactly in the center, kind of off to the side a little bit in the gestational sac.

It actually helps transfer some nutrients to the embryo during the first trimester. And some early hematopoiesis actually also happens in the yolk sac. It will shrink and disappear by 12 weeks, but most of your patients that you're kind of deciding whether or not there's a IUP or an ectopic are going to be in that 5, 6, 7, 8 week range.

So hopefully you will see a yolk sac before it disappears. And once it's disappeared, there'll be many other things to prove that it's an IUP. This is a picture of a yolk sac. So you can kind of see that gestational sac with that hyper-echoic or echogenic, I should say, rim. and the yolk sac within it kind of off to the side, not right in the center.

So if you see this, you're good. You can stop unless there's a history of in vitro fertilization, IVF, fertility treatments, things like that. And we'll talk about that. So the kind of next thing you'll see is fetal pole and embryo and transabdominal ultrasound.

You should start to see this by around six to seven weeks. A fetal pole is defined as a thickening or small mass at the margin of the yolk pack but by seven weeks it becomes not just a small mass at the margin but it actually becomes its own distinct structure. but it starts off as just kind of this bud off of the yolk sac.

If you see this, also great, this is definitive evidence of an IUP. So you can kind of see this is probably more of a six-week embryo, whereas once it starts to grow a little bit more, it becomes a little bit more of its own distinct entity off of the yolk sac and known more as a fetal pole at this point. Cool, okay. fetal cardiac activity. So we've covered before, and you may have heard in some introductory ultrasound lectures about the ALARA principle, that is as low as reasonably achievable.

So the idea is that Doppler, when you use Doppler with ultrasound, you have much higher energy levels than when you use just B-mode or M-mode. And so... fetuses and embryos are particularly susceptible to potential harm from Doppler, from energy, which is why M-MODUS preferred over pulse wave Doppler. And so how you'll measure fetal cardiac activity, and we'll take a look at a couple of clips after this, but to kind of go through the steps first, you'll locate the fetal heart and it should be kind of this little beating thing within the fetal pole and optimize your depth. So if you can get a view where the fetus is kind of more anterior, that's preferable.

Kind of reduce your depth as much as possible. And then there's actually a zoom function you can use on most of the ultrasound machines. And zooming in on the fetus will also kind of help you get your M-mode cursor right over the heart and get a more accurate reading. Then you'll place your cursor over the heart and activate M-mode.

Then you'll use the calculation package on your machine to kind of place two vertical cursors at each heartbeat and the machine should give you a fetal heart rate. So to kind of demonstrate that here's a fetus and if you can kind of take a look there is this small beating heart here and so what you do is you would place your cursor right over where you think the the heart is and you should be able to see a repeating pattern about the same depth as the the fetal heart. And so if you look on this bottom image, you can kind of see this, I'm kind of outlining it with my mouse here, this heartbeat and another one here and another one here. You want your vertical cursors to be at the same place on each heartbeat.

So either at the start or at the end is usually preferable. Sometimes if you're too close to the machine, it's difficult to make out the actual heartbeats, taking a step back. will usually help differentiate this. These are your normal fetal heart rates for gestational age. So around six to seven weeks is when you'll first be able to start seeing it on transabdominal.

So that's why I haven't listed anything prior to this. But your fetal heart rate will be around 100 to 120, and then eight weeks, 140s to 170s, and then 120 to 160 is kind of the normal fetal heart rate after nine weeks. Okay. ectopic pregnancy.

So the idea with ruling in intrauterine pregnancy is that it's much, much easier to rule in an intrauterine pregnancy than to find hard evidence of an ectopic because with transabdominal ultrasound, which is what the majority of emergency departments are using, the adnexa are just so hard to evaluate. Even with transvaginal ultrasound, it's much easier to rule in an IUP than to rule in an ectopic. However, in saying that, there are some features.

and some signs that you can use to help identify a ectopic pregnancy. The majority are going to be found in the fallopian tube and the ampullary region of the fallopian tube, but they can be found almost anywhere in the myometrium, in the abdomen, in the cornea, which is where the fallopian tubes meet the uterus, really anywhere. So if you Rulin and IUP don't try to find the ectopic unless, like I said, they're on in vitro fertilization or other fertility treatments that make something called a heterotopic pregnancy, which is the presence of an IUP plus an ectopic somewhere else, much more likely.

So if you have a positive pregnancy test, then your uterus is empty. The next thing you would do in a stable patient would be to look for some of these signs. I would argue the first thing you should do is actually the third thing that's listed here.

Look for intraperitoneal free fluid. um, hepatorenal space fluid is pretty highly sensitive for ectopic, but really any peritoneal free fluid should raise suspicion. You can look for something called a tubal ring sign, which is a thick hyperechoic ring around the tubal mass.

This is the most specific for ectopic, 95%. And then there's something called the ring of fire sign, which is based around the idea that ectopic pregnancies have a high vascular region around them. And so you can look for high velocity flow on cholera Doppler surrounding them. This is the...

tubal ring sign. So you can kind of see this this ectopic here with very thick echoes around it. Okay and then this is going to be your ring of fire sign.

So this is a visualization of the right indexa and you can kind of see with color doppler that there's lots and lots of flow around here. This is not to be mistaken with a with a corpus gluteal cyst, which can have a similar appearance to a tubal ectopic. It can actually have a similar appearance to both a tubal ring sign and a ring of fire because both a corpus gluteal cyst is going to have lots of vascularity as well. And it's going to be kind of a ring in the, in and around the adnexa. So how you differentiate this is the corpus gluteal cyst is going to have less echoes.

It's going to be a bit thinner. And the fluid inside is going to be clear and anechoic. And there's not going to be any stuff inside. So no yolk sac or fetal pole.

And so this is a corpus luteal cyst. And you can kind of see there's more anechoic fluid inside. It's a bit thinner than that tubal ring that we saw earlier. This is much thicker.

However, I should say that these kind of more specific signs for ectopic are things that you should look for in more stable patients, at least hemodynamically stable patients. Because if you have an empty uterus, a positive pregnancy test, even without looking for free fluid, I think that, you know, an unstable patient should be, you should be getting a surgical consult or an OB consult for that. With free fluid, an OB consult becomes much more, much more readily obtainable.

but you should be calling right away. With a stable pregnancy, a stable patient rather, you can look for some of these things and they can help figure out what's going on. Okay, so some other kind of just a couple of things that can come up with first trimester pregnancy ultrasound. You can have a molar pregnancy and this is kind of that snowstorm appearance where um your HCG level is significantly elevated out of proportion and you don't see any sort of intrauterine fetus or embryo or anything else.

This is obviously not viable and you would reach out with an OB consult to get this evacuated. And then just wanted to share a quick fun picture of twins. So you can kind of see this uterus with a couple little fetuses inside.

And that's all I have. So some of the key takeaways are that you always need to be ruling in intrauterine pregnancy with any pregnant patient, especially if they are hemodynamically unstable, you need to be going to the ultrasound first and foremost.

Transcript for:Understanding First Trimester Ultrasound

Transcript for:
Understanding First Trimester Ultrasound