Mistakes to Avoid in the First Trimester - SD

Mistakes to Avoid in First Trimester Ultrasound

I am Dr. Peter Dle. I am professor of radiology at the Brigham and Women's Hospital and Harvard Medical School, and I'll be speaking today on mistakes to avoid in first trimester ultrasound.

In this lecture, I'll be talking about a variety of mistakes to avoid in first trimester ultrasound. The kinds of mistakes that I'll be talking about are ones that if you do make them, they could have potentially very serious consequences either to the pregnancy or to the mother.

Misdiagnosis of a Gestational Sac as a Pseudo Gestational Sac

The first mistake that I'll talk about is misdiagnosis of a gestational sac as a pseudo gestational sac. The kind of mistake that I'll be talking about is the following incorrect statement that might be made in a particular case.

The patient has a beta HCG of 1200 milli international units per ml, and ultrasound shows a non-specific intrauterine fluid collection, one that has no visible embryo yolk sac, no double sac sign, no intertidal sign. Since there are no sonographic features of a gestational sac, the fluid collection is likely to be a pseudo gestational sac, and the patient should be treated for ectopic pregnancy.

This would be a mistake as all discussed over the next several slides. Here are some examples of that mistake before I talk about how to avoid it. And this is these next couple of slides are real life cases where this mistake was made.

The two images on the left demonstrate an ultrasound. This is a sagittal view of the uterus. This is a view through the left adnexa. This was done as a five week scan for pelvic pain, and it was read as a four by three millimeter fluid space in the uterus. That's this one, a small amount of free fluid that's here, and a 1.3 centimeter cyst adjacent to the left ovary. And the impression was left ectopic pregnancy with a pseudo gestational sac in the uterus. So they considered this little intrauterine fluid collection to be a pseudo gestational sac. The patient was treated with systemic methotrexate for the presumed ectopic pregnancy. She had a repeat scan done four days later, and on the repeat scan, an intrauterine pregnancy with a yolk sac was seen. So this little fluid collection that they thought was a pseudo gestational sac was actually a gestational sac. They only learned that four days later, but unfortunately, it had been treated with methotrexate. The woman had been treated with methotrexate, which damaged the intrauterine pregnancy. And the outcome, therefore was a failed pregnancy leading to a malpractice lawsuit. Because of this early pregnancy mistaken for a pseudo gestational sac was treated with methotrexate.

This was another example of a similar kind of mistake. The image that you see on the left side of the slide was from a five week scan done for pelvic pain. And the reading on this was thickened irregular endometrium with cystic spaces, no gestational sac identified consistent with molar pregnancy. So they saw these two fluid collections. They thought they weren't pregnancies, but they thought the fluid collections indicated a molar pregnancy. Because of that, A DNC was performed to treat the presumed molar pregnancy. Despite the DNC, the HCG continued to rise. So methotrexate was given once a week for three months on a follow-up scan, three or four months later, the patient had, the woman had a 19 week singleton intrauterine pregnancy. So one of these two fluid collections. Presumably these were twins. They thought it was a molar pregnancy. These were twins. The DNC removed one of them, but unfortunately, the methotrexate damaged the other one of them. On a follow-up, on that follow-up scan, the 19 week singleton pregnancy had already been damaged by methotrexate given early in pregnancy. The outcome was a baby born with microcephaly and the baby died at 19 months of age. And the lawsuit, the physician who interpreted this as a molar pregnancy said, I didn't diagnose an intrauterine pregnancy because there was no double sac sign. Double sac signs don't have to be present with intrauterine pregnancies because of problems such as the ones that I showed you on the two prior slides.

I, together with Dr. Carol Benson, wrote an editorial called First Do No Harm to Early Pregnancies. Early pregnancies, such as the one that you see right here that are little fluid spaces in the uterus that have no yolk sac or embryo. They're too early for that. No double sac sign, no intertidal sign. They're just a non-specific fluid collection. That's what a lot of early pregnancies look like. You can't mistake those for pseudo gestational sac or you'll get into your cause damage and get into trouble.

So the sonographic signs of early pregnancy are shown on this schematic diagram. Here is the pregnancy. This is the gestational sac. You can see there's a rim of decidua. There's another layer of decidua. There's at least a couple of layers of decidua separated by the flattened potential space of the uterine cavity. That appearance leads to an ultrasound, to some cases, a double sac sign. This is the gestational sac, and there's a rim of decidua and another rim of decidua. These are these two rims that give you the double sac sign. Or sometimes if the cavity is completely flattened and straight, you will see a gestational sac sitting adjacent to a thin white line, which is the intradecidual sign. So those are two sonographic signs of early pregnancy, but there's a third appearance that intrauterine pregnancies can have, and that's no sign or a so-called non-specific fluid collection. Not all pregnancies, in fact, about half of pregnancies early on at about five weeks scan, transvaginally will have no double sac sign, no intertidal sign of no sign at all. But don't think that it's not a pregnancy because there's no sign.

So, here for example, you see a double sac sign shown on the left. There's fluid collection, a rim of decidua, another rim of decidua. This is an intradecidual sign where you see the gestational sac and the thin collapsed uterine cavity. When they're there, fine, it's a pregnancy, but when they're not there, it still is likely to be a pregnancy.

So when you see a nonspecific intrauterine fluid collection in a woman with a positive beta HCG, a positive pregnancy test, and by a non-specific intrauterine fluid collection, I mean one that has oval shaped with curved edges. There's no double sac sign, no intertidal sign, no yolk sac, no embryo. Is it a gestational sac or is it a pseudo gestational sac?

Here are two non-specific, two different patients. They have a positive pregnancy test, and we see a little fluid collection in the uterus. Here we see another one here. There's no double sac sign, no intertidal sign, no yolk sac, no embryo. Are these gestational sacs or pseudo gestational sacs? Well, on follow-up, each of them had an embryo with a heartbeat as seen here or here. So both of these turned out to be gestational sacs. We know that 11 days or seven days later, how were we supposed to know whether this was a gestational sac or a pseudo gestational sac on the initial scan?

Well, let's do a little math. When you see a non-specific fluid collection in a woman with a positive pregnancy test, let's look at how likely it is to be a gestational sac versus a pseudo gestational sac. If we assume that the incidence of ectopic pregnancies in all pregnancies is about 2%, and that's the current percentage in the United States, if you also assume that a double sac sign or intertidal sign occurs in half of intrauterine pregnancies, but the other half are non-specific, and if you assume that a pseudo gestational sac occurs in 10% of ectopic pregnancies, which I think is actually overly high, but some articles in the literature suggest that it may be that high. If you take those three numbers and do a little bit of calculation on them, you put them into a calculator, you come out with the conclusion that a non-specific fluid collection in a woman with a positive pregnancy test has a 99.5% likelihood of being a gestational sac. 199 chances out of 200 of being a gestational sac, only one chance in 200 or a half a percent chance of being a pseudo gestational sac. So those non-specific fluid collections, like I showed you on the prior slide, are over 99% likely to be a gestational sac.

Well, there's an expression that says, when you hear hoofbeats, think horses not zebras, think of the common things, not the rare things. The gestational sac is the common thing. When you see a non-specific fluid collection, the pseudo gestational sac depicted on the right little fluid in the uterine cavity is the rare thing, the zebra. So when you see a non-specific fluid collection, think gestational sac, not pseudo gestational sac.

So the takeaway message here is that in any patient with a positive pregnancy test who has a fluid collection with rounded edges in the central portion of the uterus, you have to consider it to be an probable or almost certain gestational sac, 99% plus chance of being a gestational sac. And your report should state that there's an intrauterine fluid collection that most likely represents a gestational sac or some equivalent language. Most importantly, whenever you see those non-specific fluid collections treatments that damage an intrauterine pregnancy such as methotrexate or DNC should be avoided until intrauterine pregnancy is definitively excluded. If you don't follow these rules, then you can cause damage and get into legal trouble like this poor fellow on the left side of the screen.

Over Reliance on the HCG Discriminatory Level

Okay, let's move on to another mistake to avoid in the first trimester over reliance on the HCG so-called discriminatory level. So here the mistake would be to say the following, the patient has a beta HCG of 2,500 milli international units per ml and ultrasound shows normal adnexa and no intrauterine fluid collection. Since the beta HCG is above the discriminatory level of 2000, a normal IUP can be excluded, and therefore the patient can be treated with methotrexate for possible ectopic pregnancy without concern for harming an intrauterine pregnancy. This would be this mistake is made quite commonly, to think that if the beta HCG is above 2000 and you don't see anything inside the uterus, then it can't be a normal intrauterine pregnancy. If you gave methotrexate because there can't be an intrauterine pregnancy, you would be causing problems causing damage as we'll see on the next several slides.

So here's an example of a woman who came in to the emergency room at my hospital. She had an ultrasound done. She was having a little bit of pelvic pain. She had a beta HCG that was over 4336 milli international units per ml. And as you can see on this, on these two views, sagittal and coronal or transverse views, nothing is seen, no fluid collection is seen in the uterus. The beta HCG is 4,300. Does this mean that she has an ectopic pregnancy or an abnormal intrauterine pregnancy that isn't growing? She can be given methotrexate for her possible ectopic because she can't have a normal intrauterine pregnancy? Fortunately we didn't. It isn't the practice in our emergency room to give methotrexate based on the HCG on a single HCG level above the 2000 discriminatory level. Fortunately, we don't give methotrexate in those cases because look, a month later, she had a normal nine and a half week intrauterine pregnancy and ended up giving birth to a normal term baby. So the beta HCG discriminatory level or zone doesn't exclude a normal intrauterine pregnancy.

This is one example. Here's another one. This woman came in. She had an ultrasound done for pelvic pain, or she came into the emergency room for pelvic pain. Her beta HCG was a little over 2200. She had an ultrasound, no visible gestational sac. If we followed the protocol that's used in some emergency rooms, which fortunately we didn't, and we don't, this woman would've been given methotrexate because her beta HCG of 2200 was above the discriminatory zone of 2200, and there's nothing seen in the uterus. But look, six days later, there's a normal five and a half week twin intrauterine pregnancy seen, and she gave birth to normal twins. Another example of why the beta HCG discriminatory zone does not exclude a normal intrauterine pregnancy.

In fact, we looked and were this will be in press. This is an article being published in the December, 2011, edition of the Journal of Ultrasound in Medicine. We looked at our own hospital the experience between January, 2000 and December of 2010. We looked at all cases where the beta HCG was above 2000, and no intrauterine fluid collection was seen on that ultrasound. And then a positive heartbeat was seen on a follow-up ultrasound, we found nine such cases listed on the right, the ones in white. There are six cases where the beta HCG was above 2000 on initial scan where nothing was seen. And then heartbeat, one or more heartbeats were seen on follow up on all of these. The ones in white were the ones that gave birth to that led to normal live born. Six of the nine women with beta HCGs of 2000 and no heartbeat and no gestational sac on the initial scan came back with a pregnancy seen on a followup scan. Six of them had babies. The highest one is the one that I showed you with the HCG of 4,300 who ended up with a normal live born.

So our conclusions are that a beta HCG, even above 4,000, which is double the discriminatory level. Beta HCG above 4,000 and an empty uterus does not exclude a normal pregnancy outcome. If a woman is hemodynamically stable, an ultrasound doesn't demonstrate an ectopic pregnancy. The discriminatory level should not be used to guide management and seven normal babies at our hospital alone might not have been born if the discriminatory level had been used to guide patient management. So one HCG level of above the discriminatory level of 2000 with nothing in the uterus does not exclude a normal intrauterine pregnancy. And that's why it shouldn't be used to guide management that might damage an intrauterine pregnancy.

Confusion Between an Intra-Ovarian Mass and an Extra-Ovarian Mass in a Patient with a Positive Beta HCG

Another mistake to avoid in the first trimester is confusion between an intra ovarian mass and an extra ovarian mass and a patient with a positive beta HCG. So the two errors that can be made here are that a mass within an ovary, which is likely to be a corpus luteum. If there's a patient with a positive pregnancy test and a mass in the ovary, it's almost certain to be a corpus luteum, but it could be mistaken for an extra ovarian mass, which would lead to the false positive diagnosis of ectopic pregnancy. The flip side, the other error that could be made is the mass adjacent to an ovary may be mistaken for an intra ovarian mass or a corpus luteum, which would lead to failure to diagnose ectopic pregnancy.

This kind of dilemma is shown here in three different women who had ultrasounds done with a positive pregnancy test and pain. And in each case we see the ovary and a mass, we see the ovary and a mass, we see the ovary and a mass. But it's unclear whether this mass is, for example, in this case, does the ovary end here? In which case this is an extra ovarian mass and it's an ectopic pregnancy, or does the ovary is the outline of the ovary as shown here? In which case, this is an ovarian mass and it's just a corpus luteum. Similarly, if the ovary ends here, that's extra ovarian. If the ovary ends here, it's intra ovarian. And the same with this one on follow up. Two of these were ectopics and one was an intrauterine pregnancy. But how do you tell at the time of scanning when you see a mass that is right either adjacent to or on the edge of an ovary, whether it's just inside or just outside? 'cause it makes all the difference in the world just inside it's corpus luteum, just outside, it's an ectopic.

And this is an example woman had an ultrasound for pelvic pain and a positive pregnancy test. An ultrasound was done, nothing was seen in the uterus. There's the ovary, there's the ovary and there's a mass. Is the ovary go out to here? In which case, this is intra ovarian, does the ovary end here, in which case it's extra ovarian and it's an ectopic. Makes all the difference in the world, whether it's intra or extra ovarian. How do you tell the difference? Well, you tell the difference in many cases by taking advantage of the fact that ultrasound is a real time specialty, your transducer is sitting right up against the ovary, push it and see if these two this and this move together or separately. And here's what happens when we push, you can see that those two structures move separately. This is beside the ovary or an ectopic. So it's an ectopic pregnancy. If they move together, we would've concluded that it's in the ovary, probably just a corpus luteum.

Here's another similar case. A woman had an ultrasound for pain and a positive pregnancy test. As you can see in the upper image, there's the uterus, nothing in it. And in the adnexa we can see that there is this thing looks like the ovary. Here's a mass, but is it in the ovary just hanging off, protruding out from inside the ovary, in which case it's corpus luteum, or is it outside the ovary? Well, we pushed and when we push, you can see they move together. They don't move separately. So we concluded that this is probably just a corpus luteum inside the ovary, and therefore she doesn't have an ectopic pregnancy. And fortunately, we didn't give her methotrexate. She wasn't given methotrexate because we thought that this was a corpus luteum. And sure enough, on follow up, she had an intrauterine pregnancy. It was just too early to see on the initial scan.

So the way to avoid confusion between an intra ovarian mass and an extra ovarian mass is to push with the transducer and see if the mass moves with the ovary, which case it's probably a corpus luteum or moves separately from the ovary, which case it's likely an ectopic pregnancy.

Undercounting Pregnancy Number Prior to Six Weeks Gestational Age

Another mistake to avoid in the first trimester is undercounting pregnancy number prior to six weeks gestational age. And the mistake that you can make here is to say, congratulations, you have a five week singleton pregnancy, and we'll see in a minute why this is an erroneous statement that you have to be careful about.

So this is a woman we did an ultrasound. We looked she had a positive pregnancy test. We did the ultrasound. We see an intrauterine gestational sac. There's faintly visible within it, a yolk sac. So this looks like she has a singleton, intrauterine pregnancy, but actually look on follow up. Just a few days later, she actually has twins. There's two yolk sacs, two embryos. So in the first scan we told her, looks like you have one baby, but we're not completely sure. And in fact, she has two babies. These were twins that were under counted on the initial ultrasound.

Here's another case in which we did an early pregnancy. At about five to five and a half weeks, we see two gestational sacs. So we could say to this woman, you're having twins, but in fact there's a third gestational sac a week later. And in fact, within about a week or two after that, there were embryos in all three gestational sacs, and she had normal triplets. So which were under counted on the initial scan as twins.

So undercounting pregnancy number at five to six weeks gestation happens and not that infrequently because prior to six weeks gestational age, you don't yet see the embryo or consistently or the yolk sac and the gestational sac is very small. You may miss a yolk sac or a gestational sac. So realize that a pre six week ultrasound may under count pregnancy number, which would lead to an appearing twin or appearing triplet on subsequent scan.

In a study that I did together with Dr. Carol Benson, published in the Journal of Ultrasound Medicine in 1998, we found that multiple gestations were, when they happened to be scanned prior to six weeks, were under counted 14% of the time. I just showed you a couple of examples on the prior slides.

So how do you avoid this mistake in terms of assessment of pregnancy number, when an intrauterine pregnancy is seen on a first trimester ultrasound, you should always make an assessment of pregnancy number twin, singleton twin or whatever, but recognize that the final count may decrease due to the vanishing twin phenomenon, but also may increase due to what we've called the appearing twin phenomenon. So as long as you explain to the patient that the number that you're counting the pregnancy number that you're determining on a pre six week ultrasound is a preliminary estimate that may go up or down. You won't look foolish when you say, clearly it's this number and more show up on a subsequent ultrasound.

Misinterpretation of a Follow-Up Scan After Methotrexate for Tubal Ectopic Pregnancy

Continuing on our mistakes to avoid. Another mistake is misinterpretation of a followup scan after methotrexate is given for a tube ectopic pregnancy. And the mistake you can make here is to say, I'm scanning a woman who was treated with intramuscular methotrexate for ectopic pregnancy one week ago. She now presents with pelvic pain. I do an ultrasound. The adnexal mass representing her ectopic pregnancy is now larger and more vascular than it was just prior to treatment. So I'll report the scan as indicating treatment failure. This would be a mistake. Masses of an ectopic pregnancy will often increase in size and vascularity in the one to two weeks following methotrexate for ectopic pregnancy, even when the pregnancy is successful.

Here's an example. This is a woman who had an ultrasound for pelvic pain positive pregnancy test. We did the ultrasound. There was nothing in the uterus, there's the ovary, and we saw an adnexal mass, a right adnexal mass sitting between the ovary and the uterus. And we said correctly, it was the correct thing to say, this is an ectopic pregnancy. You can see that it's measuring about 1.48 or about one and a half centimeters because of the diagnosis. She was given methotrexate and was having quite a bit of pain, so was sent back for a follow-up ultrasound a week later. And on the ultrasound a week later, this mass has grown from one and a half centimeters to over two centimeters. You can see it's rounder, fuller, bigger than it was prior to methotrexate. This is 10 days later, it's quite vascular. So it would be a mistake to say this has grown and therefore methotrexate treatment that was given initially failed. You should give it again or go in and do surgery or laparoscopy. This is the typical appearance, not the appearance of failed methotrexate, but the typical appearance or methotrexate. In fact, ultrasound following methotrexate in the week or two is usually non-contributory because it usually, the mass usually increases.

So in terms of the interpretation of an enlarging adnexal mass a week or two after methotrexate treatment of ectopic pregnancy, the adnexal mass often increases in size and vascularity after methotrexate may take several weeks to resolve. So the increase in size and vascularity of an adnexal mass one to two weeks after methotrexate treatment for ectopic pregnancy should not be mistakenly interpreted as pregnancy failure.

Confusion Between a Cornual Ectopic Pregnancy and an Eccentrically Located Intrauterine Pregnancy

Another mistake to avoid is confusion between a cornual ectopic pregnancy and an eccentrically located intrauterine pregnancy. So this is schematic diagram of a cornual ectopic pregnancy. There's the body of the uterus and the endometrium or decidua of the body of the uterus. There's no pregnancy there, but there is a pregnancy in the cornua of the uterus. This is a cornual or interstitial ectopic pregnancy. Note that it's very eccentric relative to the right to left side of the uterus. This is the middle. It's way off to the side, but you can get pregnancies off to the side. In other situations, you can get a pregnancy. Sometimes the uterus is normal, but the pregnancy, instead of bulging inward bulges a little outward. And it's so you get an eccentric pregnancy, but it's within the uterus, it's just a normal pregnancy. And as this grows, it will grow into the center. Another situation that you can have an ultrasound that's eccentrically placed relative to the left to right side of the uterus is if you have a bicornuate uterus as shown here, or a septate uterus. In all these three cases, the pregnancy or gestational sac is eccentrically located, but it's not a cornual ectopic pregnancy. This one is an emergency. This can lead to severe or even life-threatening bleeding to the mother when the cornua ruptures, these need no treatment and may well go on to a normal baby.

Just by way of example, this is a cornual ectopic pregnancy. There's the body, the decidua or endometrium in the body of the uterus. Way out on the left side of the uterus, there's a gestational sac, and you can see that it bulges the edge of the uterus and that the bright echogenic tissue around it extends all the way out to the edge, serosal edge of the uterus. This is abnormal. This a cornual ectopic pregnancy. You can see here there's a heartbeat. There's a live embryo in it, but the echogenic tissue around the pregnancy extends all the way out to the edge. This is not intrauterine. This is in the cornua. This is a cornual ectopic.

On the other hand, what we see here is an eccentric pregnancy, an eccentric intrauterine pregnancy in a normal uterus. And the difference here is that the bright tissue called trophoblastic tissue doesn't extend all the way out to the surface. There is myometrium around the edge of the pregnancy here. So this is just an intrauterine, an eccentric intrauterine pregnancy in a normal uterus. And in fact, two and a half weeks later, it had moved into the center. Everything looked completely normal.

So you have to distinguish by looking at whether it bulges and whether there is myometrium around the edge. Again, on the here we have on the left, this is a cornual ectopic pregnancy. The bright trophoblastic tissue extends all the way out to the serosal surface here, and also on the video clip where you see the live baby, but you see the trophoblastic tissue extending out to the serosal surface. On the other hand, these are three different eccentric pregnancies here on the right side, this is a septate. This turned out to be a septate uterus, but there's myometrium around here. This was a bicornuate uterus with myometrium around it. This was a didelphic uterus. There's myometrium around it. These are all these pregnancies are eccentric, but only this one is a cornual pregnancy.

So the diagnostic criterion to avoid this mistake is if you see an eccentric gestational sac bulging the uterine contour with little or no visible myometrium, which is hypoechoic tissue around the superior or lateral aspect, it's a cornual ectopic. If you see myometrium around the entire gestational sac, it's an intrauterine pregnancy, maybe in a duplicated uterus like a septate or bicornuate or maybe not. But in any case, if you see myometrium around the entire gestational sac, it's an intrauterine pregnancy. If you're not sure and the patient is stable, 3D ultrasound with coronal reconstruction can be can give you the answer or you can try following up.

These are two different women. The ultrasounds look pretty similar. In both cases. You see an eccentric sac bulges a little bit. The bright tissue clear, looks like it's coming to all the way to the serosal surface here. It may also be. So these two these are two different women. The ultrasounds both are the same. But when we did 3D ultrasound with coronal reconstruction, here you can see that the gestational sac, this is this gestational sac on a coronal reconstruction from a 3D sonogram, is in the cornua. That's cornual ectopic. This one clearly is continuous with the endometrium and the body of the uterus. It is a intrauterine pregnancy that happens to be off to the side. And this one had to be treated and this one didn't because she had an intrauterine pregnancy and she looked completely normal on follow up. A few weeks later.

Confusion Between a Cervical Ectopic Pregnancy and a Spontaneous Abortion in Progress

Another potential confusion is between a cervical ectopic pregnancy and a spontaneous abortion in progress. Cervical ectopic pregnancy is implanted in the cervix. And this is an ectopic, it's emergent, it's an emergency situation. This can lead to severe bleeding if you don't do anything. In fact, if you just try to scrape it out, there could be very severe bleeding, life-threatening to the mother in this case. Spontaneous abortion in progress is when the pregnancy started up in the body of the uterus, but is now passing on its way, passing out through the cervix. This is a spontaneous abortion progress passing through. This is implanted in the cervix or cervical ectopic. This is an emergency situation. This is not nearly as emergent and requires no serious treatment. 'cause it will come out on its own.

So how do you tell the difference? Well, schematically note that a cervical ectopic pregnancy is likely to be a normal appearing gestational sac often has an embryo, may have a heartbeat, whereas a spontaneous abortion in progress is a flattened irregular sac that's sitting in the cervix.

Here are two examples. This the case on the left, these are, this is one case where on sagittal view, you see the pregnancy inside the cervix, and it looks like a normal gestational sac. It has an embryo with a heartbeat. The only thing abnormal about it is that it's sitting in the cervix instead of the body of the uterus. This is a cervical ectopic pregnancy. On the other hand, here you see a flattened gestational sac little material in it, what looks like a yolk sac, but no heartbeat. This is a spontaneous abortion in progress.

So the diagnostic criteria to use here to make the distinction between a cervical ectopic and a spontaneous abortion in progress are, if you see a well-formed gestational sac in the cervix with a prominent echogenic rim around it, especially if you see a live embryo, it's a cervical ectopic pregnancy. If it's a flattened irregular sac with thin or absent echogenic rim and there's no live embryo, you're dealing with a spontaneous abortion in progress. If it's equivocal, if the ultrasound findings aren't clearly this or this, you can wait one or two days. If the ultrasound findings are equivocal and the patient is stable, you can wait a day. And if it's unchanged, you're dealing with a cervical ectopic pregnancy. If it's changed or absent, you're dealing with a spontaneous abortion in progress.

Here's an example. This on the initial scan, here in the body of the uterus, we see nothing in the cervix. We see a gestational sac, there's an embryo, but no heartbeat. There isn't much of a decidual reaction or echogenic rim around it. We thought it was probably a spontaneous abortion in progress, but we weren't completely sure. So we waited and shortly thereafter on follow-up, the gestational sac was gone. So this was a spontaneous abortion in progress where the diagnosis was made by serial scans suspected on the earlier scan proved by serial scans.

Failure to Diagnose a Cesarean Scar Implantation

Yet, another mistake to avoid in the first trimester is failure to diagnose a cesarean scar implantation, a gestational sac implanted in a cesarean scar. The distinction we're trying to make here is between a pregnancy and a cesarean section scar as compared to a spontaneous abortion in progress or a low implantation of a pregnancy. This one is an urgent situation because pregnancy in a cesarean section scar that's all the way up into it and up to the serosal surface can lead to uterine rupture as it grows. So is a very different situation than a spontaneous abortion and progress or low implantation.

So the diagnostic criteria for a c-section scar implantation is the patient has a prior cesarean section. The gestational sac is located low and anteriorly in the uterus just above the cervix where the scar is, in other words, and the gestational sac and the surrounding echogenic rim, which represents trophoblastic tissue, extends to the serosal surface of the uterus.

And this is an example of a cesarean scar implantation. You can see here the cervix ends around here. So the gestational sac is low in the uterus just above the cervix. It looks like it's extending with a bright tissue all the way up to the serosal surface. When you look closer on this closeup view, you can see the bright echogenic trophoblastic tissue is actually extending not only up to the serosal surface, but even bulging it. This is a cesarean scar implantation.

Now the reason these are emergent and have to be treated is you can see on this sequence of scans, this is a woman who had we diagnosed a cesarean scar implantation at five and a half weeks. The cervix ends around here, low in the uterus is a gestational sac. The trophoblastic tissue is extending up to the towards and probably all the way to the serosal surface. We suggest that this woman be treated. One of the possible treatments is to inject potassium chloride or methotrexate into the gestational sac. But the woman declined when she came back two weeks later, you can see it's grown. There's an embryo, but now it's starting to bulge that surface. And she was having quite a lot of pain. And we said, really, we strongly suggest that you treat this probably by injection into the sac so that the sac will then stop growing and shrivel up, because you may rupture your uterus. She said no. And four weeks later, you can see it's now she was having very severe pain bulging the uterus, and she actually came to require a hysterectomy to save her life at this point. Whereas a less invasive treatment earlier would have saved her uterus.

So these are important findings to diagnose and consider management early on.

Incorrect Follow-Up of First Trimester Bowel Herniation

Another mistake to avoid in the first trimester is incorrect follow up of first trimester bowel herniation. Two mistakes you can make here, or one would be to say, bowel herniation at 10 to 12 weeks is part of normal embryologic development. So I always report it as normal. If you always report first 10 to 12 week bowel herniation as normal, you'll miss the odd case of omphalocele that comes to you on a for a 10 to 12 week scan. The other mistake you make in the other direction is would be to say 10 to 12 bowel herniation at 10 to 12 weeks, occasionally represents an omphalocele. So I always recommend a follow-up scan to roll out omphalocele, this would lead to all sorts of unnecessary scans and worried mothers who are scanned at 10, 11, 12 weeks, who are told they may have an omphalocele, but will need to check you in a few weeks to see. So to never do a follow up or always do a follow up would be a mistake.

Here at about 10 and a half weeks, you can see a mass protruding from the anterior abdominal wall seen here and here. Do we need a follow up? No, this is just physiologic bowel herniation. If she did have a follow up, not for that reason, for a fetal survey, and you can see that the umbilical cord insertion site's completely normal at that point. This was just physiologic bowel herniation. We didn't warn the mother that she may have an omphalocele and needed a follow up because we were confident that it was physiologic bowel herniation.

So how do you tell you don't want to follow these all up, but you don't wanna miss the omphalocele that comes through? Well, to answer the or avoid the mistake, let's summarize the relevant literature, which says that in the normal fetus, an echogenic mass protruding from the abdomen is seen between about eight and a half and 10 and a half weeks. Almost always 10 and a half to 12 weeks sometimes, and greater than 12 weeks, virtually never in the upper limit of normal for maximum diameter of the protruding mass is about seven millimeters. So this gives us a clue as to how what our recommendations should be. And they're shown here, if you see an echogenic mass protruding from the anterior abdomen, and it appears prominent at eight to 12 weeks, measure it. And if the measurement either anteroposterior or transverse diameter is less than seven millimeters just to report the scan as normal and no need to re-scan, like in the case that I showed you a slide or two ago. On the other hand, if it's greater than seven millimeters greater or equal to seven millimeters, then it may be an omphalocele and she should be re-scanned in the second trimester to roll out omphalocele.

So here's a case where the maximum diameter, here's a herniated mass. The maximum diameter is less than seven millimeters. It is about five and a half in both dimensions as well as about five millimeters across transverse. This is normal. This should be reported as normal in this, no need to re-scan. On the other hand, here are two different women with where the herniated mass is measuring over seven millimeters. Here it's about 12, 11 or 12. Here, it's a little over seven millimeters. These went on the, in the infrequent case that they're over seven millimeters, we recommend a re-scan for possible omphalocele. This one had one on follow-up. This is an omphalocele, and this patient on follow-up has a nice normal cord insertion.

Failure to Recognize Implications of a Slow Fetal Heart Rate Even After Normalization

So another mistake to avoid in the first trimester on our long list of mistakes, it relates to the fetal heart rate. Early on, when the heart rate is slow between six and seven weeks of gestation, there's a fairly high chance that the embryo, that the heartbeat is gonna stop, that the embryo will die. Slow heart rate is a bad finding indicating a high likelihood of subsequent fetal death. So when we see a slow heart rate, heart rate, we recommend a follow up ultrasound. And most of the time with a slow heart rate, the follow up ultrasound will show no heartbeat. But what if the slow heart, what if the heart rate is slow on a scan today, we recommend a follow up in 10 days, let's say a week or two later, she comes back and the heart rate's normal. Does that mean that the risk is gone?

So in fact, it doesn't. And the mistake would be to say the embryonic heart rate, which was slow a week ago, is now normal. So the pregnancy for the prognosis for the pregnancy is fine. That unfortunately is not the case. Here's an example. A woman had a slow heart rate under 90 beats per minute at six weeks. Here it is actually going at 89 beats per minute. It's a little slow. So we said heart rate's slow, we're worried about the prognosis for the pregnancy. Suggested a follow up at about a week and a half later. At 7.7 weeks, she came back. Now the embryo's grown. The heart rate is fine. It's in the mid 100, it's 163 beats per minute. Does that mean that she is, her prognosis is fine. We were worried here, but now it's fine. Well, the answer is this worrisome finding. Even when the heart rate's normal, she, her chance of demise is still somewhat elevated. And notice that at about 10 weeks there is fetal demise.

So unfortunately, when the rate is low on the initial scan, follow-up scan with a normal rate, doesn't mean that the chances are completely normal. We did a study at our hospital published a few years ago, and when the fetal heart rate is slow on the initial scan and then follow up is normal, there was still a 25% chance of demise, which is still pretty high.

So you wanna avoid false reassurance when a slow heart rate reverts to normal on a follow-up scan. When a slow heart rate is seen at six to seven weeks, the embryo is at increased risk of demise by the end of the first trimester. Even if the heart rate is normal on a follow-up scan, one to two weeks later, the risk of demise by the end of the first trimester remains high about 25%. When is the woman out of when does the increased risk end? The answer is that if you have a slow heart rate early on and the fetus is still alive, there's still a heartbeat at the end of the first trimester at 13 weeks, then the risk reverts to normal.

Failure to Recognize a Thick Nuchal Translucency

And yet, another mistake to avoid is failure to recognize a thick nuchal translucency. The two mistakes you could make here is would be I'm doing a 12 week scan on a patient who isn't planning to have a serum screen. So I'll ignore the nuchal translucency, or I'm doing a 12 week scan and I'm not NT certified, so I'll ignore the region behind the fetal neck. You should always do as complete a evaluation on any ultrasound that you do. And that includes looking at the fetal neck, even if the woman isn't having a serum screen or you're not NT certified.

Here's a nuchal scan on a fetus at about 12 to 13 weeks, apparently normal fetus. Say she's not planning to have a serum screen and or you're not certified, does it mean you shouldn't look at the region behind the neck? Not at all. And if you look carefully at the region behind this fetal neck, you'll see I don't see the second line I should be seeing. You normally see another line in here, which is the skin surface making you wonder whether this whole thing is a thick nuchal translucency. And in fact, when the baby jumps up, you can see that she has a thick nuchal translucency that led to concern that she might have a chromosomal abnormality. And in fact, this fetus turns out to have Trisomy 21.

So don't ignore looking at the nuchal translucency, looking at the region behind the fetal neck. In cases when a woman isn't planning to have a serum screen, or if you're not NT certified, here are four different fetuses with thick nuchal translucency. This one proved to have Trisomy 13, trisomy 21, and this one, this one had demise two weeks later after the thick nuchal translucency. In this one, even though the nuchal translucency is very thick, over five is normal. So there the nuchal translucency doesn't tell you what the outcome has to be. And in fact, it can be normal, even with a thick nuchal translucency. But the risk is high and you should always look at it regardless of the situation.

Conclusion

So I've come to the end of the tour of mistakes that can be made in the first trimester. Making these mistakes can lead to bad outcomes, to the embryo or fetus or bad outcome to the mother. You really want to avoid these mistakes, and I hope I've given you some clues as how to and about how to avoid some of these mistakes in the first trimester.