Emergency Medicine in the 2nd and 3rd Trimester - SD

Introduction

My name is Dr. Carol Benson.

I'm from Brigham and Women's Hospital and Harvard Medical School.

The title of my talk is emergency ultrasound in the second and third trimester.

I'm going to be speaking on emergency ultrasound in the second and third trimesters of pregnancy.

Indications for Emergency Ultrasound

Emergency ultrasounds may be required in several situations.

They may be required because the patient has symptoms such as bleeding, pain or cramping.

They may be required because of an abnormal physical finding on an examination with a clinician such as the shortened cervix or elevated maternal blood pressure, or they may be required when there's concern for the fetal wellbeing, such as decreased fetal movement or abnormal fetal heart rate patterns.

Evaluation of Bleeding in the Second and Third Trimester

When bleeding occurs in the second and third trimester, ultrasound is used to assess for placental abruption and placenta previa.

Placental Abruption

A placental abruption is premature separation of the placenta.

It occurs in about 1% of all pregnancies, and it is the most common cause of intrapartum fetal death accounting for 15% of perinatal mortality.

It also may cause problems for the mother, including maternal coagulopathy.

The mother typically presents with symptoms of pain, bleeding, and sometimes contractions.

The ultrasound findings when a patient has an abruption can be normal.

This is found in about 20% of cases.

In 80% of cases an hematoma will be identified in the vicinity of the placenta.

It may be in a subchorionic location tracking away from the placenta.

It may be behind the placenta, or it may be in a preplacental location with the blood tracking anterior or on the amniotic side of the placenta.

In addition, echoes may be seen in the amniotic fluid due to blood that has seeped into the amniotic cavity.

Here's a retroplacental hematoma from a placental abruption.

You can see a hypoechoic lesion sitting behind this edge of the placenta, which is here and lifting up that edge of the placenta on a different view of the same abruption.

You can see this hypo irregular irregularly shaped collection beneath the placenta representing the hematoma from the abruption.

This patient has a hematoma adjacent to the placenta.

You can see the placenta here posteriorly, and then adjacent to it is a lesion that has almost the same echogenicity as the placenta and might be confused with an extension of the placenta.

If, however, we add power doppler to the image, you can see that while there's some flow inside the placenta, there's no flow in this homogeneous mass that is a hematoma, but looks like a placenta, and we can confirm the fact that it's not the placenta by watching this hematoma move when the baby kicks it, you can see it's a gelatinous type substance that jiggles as the baby's extremity bumps up against it.

This patient also has an abruption and developed a preplacental hematoma.

You can see this crescentic collection anterior or not anterior, but in the amniotic side of the placenta.

And notice how it too has a gelatinous type appearance that jiggles as the baby kicks the hematoma.

Placenta Previa

Placenta previa occurs when part of the placenta or all of the placenta covers the cervix, and in particular, it may cover the internal cervical os, or it may extend close to the internal cervical os covering part of the internal surface of the cervix.

If you look at the obstetrical definitions of placenta previa, they're listed here.

A complete placenta previa occurs when the placenta covers the entire internal cervical os.

A partial placenta previa occurs when the placenta partially covers the internal os.

A marginal placenta previa is defined as occurring when the placenta ends at the margin of the internal os, and a low lying placenta extends close to but does not abut the internal os.

Unfortunately, ultrasound cannot be as precise as these obstetrical definitions.

Why not? Ultrasound cannot determine the exact location of the internal cervical os.

It cannot determine the exact extent of placental implantation versus overlap of some of the placental tissues against other tissues.

So as a result, ultrasound cannot distinguish marginal from partial previa.

So for practical purposes, ultrasound terms should be limited to complete placenta previa, marginal placenta previa, and low lying placenta, and the term partial placenta previa should be avoided.

A complete previa is when the placenta covers the entire cervix, a marginal previa when the placenta covers part of the cervix and a low lying placenta when the placenta covers only a part of the cervix earlier in pregnancy.

Marginal versus low lying placenta, both of those terms can be used for placentas that extend close to the cervix, but do not cover the internal cervical os in practice.

Whichever one you use, remember to report the distance from the edge of the placenta to the internal cervical os.

A complete placenta previa occurs when the placenta covers the entire cervix.

That is, it covers the internal cervical os and extends beyond it.

Some placenta previas that are complete or central and some are asymmetric.

When there's central, the placenta is centered over the cervix, and when they're asymmetric, a large part of the placenta is on one side of the cervix while a smaller portion extends to the other side.

So here is a central complete placenta previa.

You can see on this view of the lower uterine segment that we have placenta along the anterior surface of the lower uterine segment, crossing the cervix and extending posteriorly.

You can see the cervix beneath the placenta with the internal os marked with the arrow on the gray scale and the color view and the cervical canal extending down from that point.

Okay, with marginal or low lying placenta, the placenta covers part of the cervix.

Here's a case of a low lying or marginal placenta previa.

You can see that the internal os is marked with the arrow and that the placenta ends close to the internal os less than two centimeters.

Notice also with the color doppler that the hypoechoic areas that you see at the edge of the placenta are actually vessels, some of which are part of the placenta.

This is a transvaginal view of the placenta and the cervix showing another low lying placenta.

You can see the cervix and the cervical canal.

The calipers are placed on the internal cervical os and the edge of the placenta as we see here.

And you can see that the distance from the edge of the placenta to the internal cervical os is only 1.3 centimeters.

Scanning Techniques and Pitfalls for Placenta Previa

Transabdominal scanning is the first way to assess for placental previa, but it doesn't always work.

The reason for the pitfalls of abdominal scanning are listed here.

You may have placental vessels that mimic a membrane separation when in fact there is blood flowing in those vessels.

You may have a lower uterine segment contraction.

If the maternal bladder is overly filled, that will limit the transabdominal scan and very often the fetal head will be overlying the cervix obscuring it.

Here's an example of a contraction mimicking a placenta previa.

At 8 32 in the morning, this patient was scanned and the anterior placenta appeared to extend close to the what looked like the internal cervical os.

And here you can see what looked like the cervix.

But by 8 56 now you can see that now that we have a better view of the placenta and the contraction has disappeared, the placenta is far from the cervix ending well away from it and no evidence of a previa.

Here's the transvaginal scan a few minutes later, again, showing the cervix, the internal cervical os and no evidence of placenta anywhere near the cervix.

On transabdominal view, sometimes the fetal head will obscure the cervix.

You can make an effort to lift the fetal head to try to get a view of the cervix, and then if that fails, of course you can do a transvaginal scan.

In this case, we could not see the cervix because of shadowing from the fetal head, but we put pressure on the fetal head and you can see that with the pressure, the fetal head is lifted and this patient actually has a placenta previa.

You can see the cervix here, the internal cervical canal and the placenta overlapping and attached to the edge of the cervix.

Now, if the transabdominal scan is inconclusive, a transvaginal scan should be performed unless it is contraindicated, in which case a translabial scan can be done.

Here's a patient who had a transabdominal scan.

You can see that the evaluation of the placenta was not possible because the fetal head obscured this posterior placenta, but a transvaginal scan was performed and you can see now a good view of the cervix, the internal cervical canal and the internal os, and you can see that the placenta extended all the way up to the internal cervical os.

Vasa Previa

Now another form of previa, something called a vasa previa.

This occurs when there's velamentous cord insertion of the umbilical cord into the lower uterine segment, and then those vessels travel beneath the membranes to the placenta crossing the cervix.

Because these are fetal vessels and they're unprotected by membranes, this is associated with a high perinatal mortality.

On ultrasound, we'll see vessels overlying the cervix, and we can confirm the vascularity with color and spectral doppler the color showing where the flow is, the spectral doppler confirming that these are umbilical vessels belonging to the fetus.

So here's a transvaginal scan of the lower uterine segment on a patient.

The placenta was not near the cervix, but look, as we pass this clip over the cervix, you can see in the clip the internal cervical canal and you can see just over the os a vessel crossing over from one side of the cervix to the other right over the internal os.

With spectral doppler interrogation of this vessel, we see that it has an umbilical artery waveform.

This is the fetal umbilical artery and you can see how dangerous this could be.

If the cervix were to open and tear this vessel, the fetus would suffer severe bleeding.

Evaluation of Pain in the Second and Third Trimester

Another reason for an emergency ultrasound in the second or third trimester is if a patient presents with pain, pain can result from abruption, from cervical changes, or if there's a uterine incarceration.

Cervical Assessment

When evaluating the cervix in pregnancy, it's important to see the entire length of the cervix, including the internal os.

The normal cervix prior to the third trimester should measure more than three centimeters, and the internal cervical os should be closed.

We measure the length of the cervix on a sagittal view that shows the cervical canal.

The internal os, as I said, must be visible and we measure the closed portion of the cervix from the amniotic fluid to the external os along the cervical canal.

Transabdominal scans are often successful at measuring the cervix, but if they're not successful, we can move on to a transvaginal scan or to a translabial scan.

If a transvaginal scan is contraindicated.

Here's a patient with a transabdominal scan at 20 weeks gestation where we got a good look at the cervix.

You can see the walls of the cervix are marked by the yellow arrows and the cervical canal is marked by the calipers showing that its length is 5.3 centimeters, well above the normal of three centimeters.

There are pitfalls to scanning the cervix transabdominally.

One is that fetal parts may overlie the cervix obscuring it.

Another is a lower uterine segment contraction.

Another is an overly full maternal bladder.

And lastly, sometimes maternal body habitus prevents our seeing the entire cervix.

Here's a transabdominal scan in a patient with a lower uterine segment contraction.

We know that the cervix is down here behind the bladder, but we have no idea where the internal cervical os is because of the contraction of the lower uterine segment such that the anterior and posterior walls of the cervix are abutting each other and touching each other, preventing us from seeing the amniotic fluid against the internal os.

If we wait a little while though, this contraction will begin to resolve and we will then be able to see the entire cervix and separate it from the contraction.

In this patient, the bladder was overly full because the bladder was full, there was opposition of the anterior and posterior walls of the uterus making the cervix look abnormally long.

You can see that part of this is the cervix and part of this are the two walls of the uterus compressing against each other.

When we empty the bladder.

Now we have a better view of the cervix.

We can see the entire length of the cervix.

It now measures 3.9 centimeters.

The transvaginal scan is usually diagnostic for evaluating the cervix in pregnancy.

We do though need to be careful because there is risk of bleeding if the patient has a placenta previa and there's also risk of introducing infection if the patient has ruptured membranes.

Here's a patient in whom we could not see the cervix transabdominally.

The patient had cramping and pain and they did want to know the status of the cervix, but the fetal head was obscuring the cervix.

We know it's down here someplace, but we don't know whether it's open or closed.

Transvaginal scan was immediately performed and you can see now that the cervix was open.

There is opening of the internal os with bulging of membranes into the cervical canal, and here we've measured the residual cervical length to be 1.0 centimeters.

Shortened Cervix and Risk of Preterm Delivery

When the cervix shortens prior to the late third trimester, there's increased risk for preterm delivery.

The normal cervical length should be more than three centimeters, so if it's less than three centimeters, it's important to note that there's an increased risk of preterm delivery.

That depends on how early the premature cervical shortening is and how much.

So there's particularly increased risk for preterm delivery if the shortening occurs before 24 weeks gestation or if it's shorter than 2.5 centimeters.

Here's the patient with a shortened cervix.

This is a transvaginal scan showing the cervix.

Here's the cervical canal marked with calipers to give a length of 2.1 centimeters.

Sometimes the internal os will open, but the external os will remain closed, and what you'll have is you'll have a funnel shaped protrusion of membranes into the upper cervical canal.

This is a diagram showing that when we have this, we measure the residual length of the cervix from the amniotic space to the external cervical os, as you can see here, and it's the residual closed portion of the cervix that helps us know what the risk is of preterm delivery.

So here's a patient with an open internal os with funneling and the residual cervical length has been measured.

You can see we have a transvaginal probe in position.

Here is the external os.

The level of the internal os is up here, but there is funneling an open funneling into the cervical canal, leaving a residual cervical length of only 1.0 centimeters.

Overall, the risk of preterm delivery is related to the length of the closed portion of the cervix.

It's not related to the width of the funneling.

The shorter the cervix, the greater the risk.

Here's some information about 24 week gestations.

If the cervical length is less than two at 24 weeks gestation, the likelihood of preterm delivery is very high.

If it measures two to 2.5, there's a moderate risk of preterm delivery.

And if it's 2.5 to three, only a mildly increased risk of preterm delivery.

So here's a 20 week gestation.

You can see that there's funneling of fluid into the upper portion of the cervical canal, and the residual cervical length is 1.7 centimeters at this gestational age.

That means there is a high chance that this fetus will be delivered prematurely.

Dynamic Cervix

In some cases the cervix changes minute to minute and thus we need to look at the cervix for more than just a single measurement.

This has sometimes been called a dynamic cervix.

When we see this, we do want to measure the cervix at its shortest measurement.

The degree of funneling will change, the length may change, but the risk of preterm delivery is related to the shortest measurement of the residual closed portion of the cervix.

So here's a patient with a dynamic cervix at 26 weeks gestation.

These are transvaginal scans done close to each other.

You can see initially we can see a portion of the cervix is closed and a portion is open and the residual cervical length and almost 1.4 centimeters.

But just a few minutes later, the funneling has widened significantly and the residual cervical length is now only 0.9 centimeters, much smaller than it was just a few minutes before.

You also can assess for a dynamic cervix by putting fundal pressure on the uterus to try to see if the cervix will open from that pressure.

This may lead to shortening of the cervix as well as an increase in the amount of funneling.

Again, the overall risk of preterm delivery after fundal pressure is related to the shortest measurement that you get from the residual cervical length.

So here's a patient who had a transvaginal scan for suspected cervical incompetence.

Initially, the cervix measured normal at 3.3 centimeters, but with fundal pressure we could see the cervix begin to shorten.

And sure enough, after some fundal pressure, the cervix was now short at 2.1 centimeters.

Incarcerated Uterus

Now I do want to mention something that's very unusual diagnosis that doesn't occur too often but can cause significant problems in the second and third trimester.

And this is something called an incarcerated uterus.

This occurs when you have a retroflexed uterus where the fundus becomes trapped behind the sacral promontory and remains trapped after the first trimester.

These patients present with pain that may be increasing over several days and the inability to urinate overall.

This is a serious diagnosis because the pregnancy loss rate is as high as 33%.

The treatment for incarcerated uterus before 20 weeks gestation is to attempt to reposition the uterus so that the pregnancy can continue.

After 20 weeks gestation, these patients can be monitored for preterm labor and require delivery by cesarean section.

On ultrasound, the cervix will appear markedly elongated, as well as elevated anteriorly.

And the uterus and gestational sac will be trapped behind the cervix.

Often the bladder is distended and high up in the lower abdomen.

And here's a diagram of how uterine incarceration occurs.

What happens is that you have a very small space between the symphysis pubis and the sacrum, and this retroflexed uterus that has been trapped behind the cervix by the sacral promontory, and it can't extend upward where it belongs.

As the gestational sac continues to grow, it forces the cervix up against the bladder and anteriorly.

This causes bladder outlet obstruction and marked pain for the mother.

It can be a difficult diagnosis to make.

If you haven't seen a case, what you'll see is in attempts at looking for the cervix, you'll have trouble finding the cervix because the cervix will be just beneath the bladder, but the gestational sac will extend much lower.

And very often when this exists, people are looking for the cervix way down here.

This is actually the fundus of the uterus.

This is the fundus, this is the body, and this is the cervix.

It's folded over on itself.

A close look will show that the cervix is elongated in this case, measuring 6.5 centimeters.

Here's a case of twins.

This is actually a vaginal scan evaluating for uterine incarceration.

You can see the elongated cervix is anterior to the uterine fundus, which is trapped behind the cervix here.

This woman actually had twins.

It was a 16 week gestation, the twins were reduced.

And on follow-up scan the next day, you can see now the uterus is in proper orientation.

Here's the maternal bladder.

Here is the lower uterine segment, and here is the cervix with the normal cervical canal in normal position with the fundus of the uterus now pointing superiorly, extending up towards the mother's head.

And here you can see the twins up here again, the second fetus and the first fetus, both now in proper orientation.

This patient had a uterine incarceration at 30 weeks gestation.

You can see on this transabdominal view, we were attempting to find the cervix.

The cervix actually is here and very difficult to see.

And sitting behind the cervix was a fibroid attached to the fundal portion of the uterus.

This fibroid was trapped behind the sacral promontory leading to incarceration.

Here's the fibroid.

Here is the uterus, and here is an MRI of the same patient.

You can see the urinary bladder, you can see the cervix pulled far anteriorly way up here.

And then you can see the uterus flipped over such that this fundal fibroid is trapped behind the sacral promontory here.

Abnormal Physical Findings: Hypertension and Fetal Well-being

Now sometimes a patient will go to an appointment and the clinician will find abnormal findings on physical exam and the most common to shortened cervix or high blood pressure.

When mothers have chronic hypertension, this is a pre-pregnancy condition, but mothers can also develop hypertension during pregnancy called pregnancy induced hypertension or gestational hypertension.

Also, hypertension may be a sign of preeclampsia.

Ultrasound is then used to evaluate the baby to make sure that the baby is doing well.

And the parts of the baby to evaluate are to make sure there's enough amniotic fluid around the baby to make sure that fetal growth is appropriate to do a biophysical profile to assess fetal wellbeing and umbilical artery doppler to assess the blood flow to the placenta.

Umbilical artery doppler can give a clue to placental abnormalities.

If the diastolic flow is absent or reversed, there's an increased risk of perinatal morbidity and mortality.

So here is umbilical artery waveform on a fetus with absent diastolic flow.

You can see the sharp systolic peaks on the waveform with absence of flow during the diastolic portion of the cardiac cycle.

And here's a fetus who has reverse diastolic flow.

You can see the sharp systolic peaks with reversal flow in the umbilical artery in between the systolic peaks.

Decreased Fetal Movement and Abnormal Fetal Heart Rate Patterns

We also may want to assess the fetus with ultrasound if the mom presents with complaints of decreased fetal movement or abnormal fetal heart rate patterns at the time of doppler examination.

Abnormal fetal heart rate patterns may be seen with non-reactive non-stress tests where they may have variable decelerations or even arrhythmias.

With ultrasound, it's important to assess the amniotic fluid volume whenever there are abnormal heart rate patterns because the abnormal heart rate patterns may be due to cord compression.

And this can occur when there's oligohydramnios cord compression can also occur with a nuchal cord or with cord presentation.

Nuchal cords are actually present at delivery in 16 to 30% of all deliveries, and the incidence increases with gestational age.

They start at a single, but they may be double or even triple as gestational age progresses.

And what we will see are umbilical vessels encircling the neck.

Fortunately, most of the time, nuchal cords do not cause any adverse outcome for the fetus.

They're not associated with adverse outcomes.

If the fetal heart rate patterns are normal.

If however, there are abnormal fetal heart rate patterns, then the nuchal cord may be implicated in the cause of those abnormal fetal heart rate patterns.

So it's been shown in the absence of abnormal fetal heart rate patterns.

Nuchal cords are not associated with increased perinatal morbidity or mortality.

Meconium staining, low apgars or acidosis at birth, I have to say it's still a little bit scary.

Here are two clips of the fetal neck and you can see that there's a nuchal cord all the way around this neck.

On this view as well as on this view.

Cord Presentations

Cord presentations are when the cord is the structure that's just over the cervix.

And these can present with abnormal fetal heart rate patterns.

They can be considered an obstetrical emergency because there is risk for cord prolapse.

If the cervix were to open umbilical, the umbilical artery may be trapped in the cervical canal.

What we see on color doppler are vessels between the fetus and the cervix.

Well, here's a patient who has an open cervix, and you can see in this open cervix the umbilical cord has funneled down through with the membranes protruding towards the vagina.

Here is the color doppler showing protrusion of the cord into the open cervical os towards the vagina.

This is an obstetrical emergency.

This is a case where the mom should be put in trendelenburg and taken up to l and d for delivery.

Here's a woman who had funneling of her membranes at 19 weeks gestation.

She did have a cerclage in place and the cerclage was holding here, but when she presented at 20 weeks gestation, there was now protrusion of the umbilical cord into that funneling, and there was also protrusion of the membranes through the internal, through the cerclage towards the external os.

Fetal Arrhythmias

Now, sometimes fetal heart rates are abnormal.

There may be premature atrial contractions or supraventricular tachycardia or even heart block.

Here's a fetus who has premature atrial contractions.

This is typically a benign finding in the fetus and has no adverse outcomes.

Notice as we watch the heartbeat, we can see it's irregular.

There are a couple beats close together, and then a pause.

And we've captured this on the M mode, showing the regularity of several beats, followed by an early beat and then a longer pause.

And here again is an early beat, followed by a longer pause.

The fetus may also have supraventricular tachycardia.

As we see here, this fetal heart rate is moving very, very fast.

We've measured it on M mode to be 266 beats per minute.

Unfortunately, this is not a benign condition for this fetus.

This fetus has a pericardial effusion, a pleural effusion, and ascites.

So this fetus has developed hydrops due to the supraventricular tachycardia.

Conclusion

Well, I've given you a run through the use of ultrasound in the second and third trimester for emergencies.

I hope this will be useful to you. Thank you.