Okay, guys, super important question -- let’s focus.
A 34-year-old woman, G3P2 presents in her 33rd week of pregnancy with vaginal bleeding
that started last night while she was asleep.
She denies uterine contractions or abdominal pain.
She had a cesarean delivery in her previous pregnancy.
She reports a 10 pack-year smoking history.
Her vital signs are as follows: blood pressure is 130/80, heart rate is 84, respiratory rate is 12, and temperature is 36.8.
Examination is negative for abdominal tenderness or palpable uterine contractions.
The patient’s perineum is mildly bloody.
On speculum examination, no vaginal or cervical lesions are seen.
A small amount of blood continues to pass through the cervix.
Which of the following findings would you expect on ultrasound examination?
Answer choice A: Partial covering of internal cervical os by placental edge;
Answer choice B: Retroplacental blood accumulation;
Answer choice C: Placental calcification;
Answer choice D: Cysts on placental surface; or -
Answer choice E: Loss of clear retroplacental space.
Now take a moment to come to the answer by yourself before we go through it together.
Okay, this is a very high-yield question.
The USMLE loves giving you any type of pregnancy complication and this one is bread and butter.
Now, this is of course a question for OB-GYN, this is OB-GYN through and through.
Now we have a two-step question that we’re dealing with.
The first thing we need to do is read the question stem carefully to figure out what’s the diagnosis we have to know
and then second, in that diagnosis, what will the ultrasound look like?
Now the stem is absolutely required because you really have to think through the physical examination
and the clinical symptoms to figure out the diagnosis.
Okay, so let’s walk through it together, let’s determine the diagnosis.
We have a female pregnant patient presenting to us in her third trimester of pregnancy
and the chief complaint here is vaginal bleeding.
Now she does not had any associated pain or contractions, that’s very important,
and also of great importance in the question stem is that she has previous pregnancies that are significant for a cesarean section.
Now the reason why that we care about this is that uterine scarring after cesarean section
makes certain complications of pregnancies in the future more likely.
Now, the differential diagnosis we have at this point really is quite variable
because it’s all based on third trimester vaginal bleeding.
Now refer to the image of where we are looking at different forms and causes of third trimester vaginal bleeding.
The first thing I want you to notice from looking at this image
is that it’s divided into both painful and non-painful causes of vaginal bleeding,
so our differential diagnosis here, the first one, which is not in this image
but I need you to know is an ectopic pregnancy,
and that’s when you have implantation of the embryo in an abnormal location inside or outside of the uterus.
Now, of the other causes here in this image in our differential diagnosis is uterine rupture.
Now you can also have placental abruption, placenta previa and also vasa previa.
These are the five things that are our differential diagnosis.
Now let’s start chopping them down and this is what you should be doing in your head.
Think of a reasonable diagnosis and then start deleting one by one ‘til you come to the right answer or at least narrow it down.
So ectopic pregnancy, throw that off the differential because that’s going to be unlikely.
Ectopic pregnancy usually doesn’t make it to third trimester
and on the routine care, you know, we would have found that earlier so unlikely.
Now uterine rupture or placental abruption is also going to be unlikely because they’re painful.
Now look at the left side of the diagram -- uterine rupture, placental abruption -
both those things have a rupture or an abruption in them,
you know, in the title and that tells you it’s going to be painful.
Now this patient has no abdominal pain, they don’t have any discomfort so this is not a painful cause of uterine contraction.
We can delete those two, also off from our differential
and really narrow down our differential to the non-painful causes of third trimester vaginal bleeding
which is Placenta Previa and Vasa Previa.
Now Vasa Previa is very rare, it’s actually fairly uncommon and that’s something that you rarely see.
Now Placenta Previa is going to be seen in some portion of the population
and it’s actually consistent with the presentation and risk factors of this patient.
She smokes, that’s something that increases the risk of Placenta Previa;
she’s had previous cesarean sections and that scarring actually increases the risk of Placenta Previa
and that’s something we’re likely to probably see here,
so the likely diagnosis is down to Placenta Previa and Vasa Previa,
and the fact that it’s more common to have Placenta Previa and the risk factors of smoking
and C-section are going to pull us to saying, okay, the most likely diagnosis here is Placenta Previa.
Now what we have to do is determine the ultrasound findings associated with Placenta Previa.
Now when you look at an ultrasound of the uterus here, what you’re going to see by definition
and how you should see it there in the image is placental insertion near or over the cervical opening
and that’s what we expect to see which is Answer choice A, partial covering of the internal cervical os by the placental edge.
Now let’s go through that explanation a bit more.
So this patient’s coming in with painless vaginal bleeding in the third trimester of pregnancy
and her condition as we just went through is suggestive of Placenta Previa
which is a condition in which the placenta fully or partially covers the internal cervical os.
Now, like we were saying previously, whenever you have patient coming in with third trimester vaginal bleeding,
you need to think of four things right away and you can split them into painful and non-painful causes of vaginal bleeding.
Now Placenta Previa, being one of the non-painful causes,
is when the placenta lies within two centimeters or overlaps the internal cervical os,
and the bleeding that we see here is a result of chronic villi interposition
between the walls of the lower uterine segment and the cervical canal.
Now, another cause is Placental Abruption.
Now this is going to be a painful cause, you know just hearing the word there -- abruption -- ouch, you know?
This is when you have normal lying placenta actually detaching from the uterus before birth.
Now the next in our differential is a uterine rupture which is of course going to be painful,
you hear the word rupture, ouch, which is going to be partial or complete disruption of the uterine wall integrity.
And last on our differential which is the most rare is Vasa Previa in which the umbilical cord vessels
actually get wedge between the fetal presenting part and the lower uterine segment.
Now, of course like I said, the clinical relevance is going to be key here in narrowing your differential diagnosis
into the painful and the painless bleeding syndromes here.
Now, like we said, the causes of painful, ouch, bleeding syndromes are going to be uterine rupture and Placental Abruption,
those all sound very painful; and Placenta Previa and Vasa Previa are going to be the causes of painless bleeding
because they have to word previa, you know, preview.
That’s not painful, there’s no pain in previewing but abruption and rupture those just sound painful so very simple to remember that.
Now, in this patient, the absence of uterine contractions is actually another factor
which allows us to differentiate Placenta Previa and Vasa Previa, with Placental Abruption and Uterine Abruption because patients,
not only will they have painful vaginal bleeding, they’ll also have associated contractions with it,
and that’s how I imagine the pain -- it’s bleeding
but there’s contractions as well from the abruption or rupture which is going to be painful.
Now, while Placenta Previa is the most common encountered cause of vaginal bleeding,
I want you to know on the other end of the spectrum,
Vasa Previa is the most uncommon cause of vaginal bleeding.
Now, and any patient that comes to you in the third trimester of bleeding,
it seemed really important to exclude Placenta Previa prior to performing a digital vaginal examination
because any contact with the placental vessels that are interpose within the internal cervical os,
can actually lead to increase bleeding when you’re doing your digital exam,
that why we do transvaginal ultrasound because that’s the best way to image
and visualize the placental location and for us to evaluate for suspected Placenta Previa.
Now, of all of the answer choices that are provided, the partial covering of the internal cervical os
by the placental edge is consistent with the ultrasound diagnosis of Placenta Previa.
Now let’s look at some of our other answer choices
and show how them how we could have eliminated those and why they’re wrong.
Now, answer choice B is retroplacental blood accumulation and that’s actually seen in Placental Abruption
which is characterized by again by vaginal bleeding, uterine tenderness, contractions and pain -
none of which is seen on this patient and again, the blood accumulation,
retroplacentally is going to be seen in Placental Abruption not in Placenta Previa.
Now, answer choice C, calcification of the placenta can actually be normal as the placenta matures
but accelerated calcifications can actually occurs in numerous conditions
and the one I really want you to remember is intrauterine growth restriction
which can be a cause of this calcification, that’s a bit early,
but not -- would not cause bleeding and it’s not related to our differential in this patient.
Now, answer choice D is surface placental cyst.
Now if they’re large or multiple they can actually cause intrauterine growth restriction which of course makes sense
because the cysts are taking up space but again, those don’t contain blood
and they don’t contain bleeding, so we don’t have to worry about them in our differential.
And Answer choice E which is the loss of clear retroplacental space, now this is a sign of abnormal placental implantation
which is going to be the differential of placenta acreta, increta or percreta;
and this can actually cause bleeding in the third phase of labor -- okay, labor -- not pregnancy,
so it’s going to be an unlikely cause of bleeding prior to labor,
so that’s going to be seen as a abnormal placental implantation in labor not in pregnancy.
Now let’s lastly review some high-yield facts. I want you to also memorize that vaginal bleeding in the third trimester
actually presents in one out of ten women, of course, in the third trimester of pregnancy,
but this is different than spotting.
Spotting happens but vaginal bleeding is actually abnormal. Now, there are multiple causes.
Now it can be an unharmful sign of labor if the patient’s appropriately going into labor, or it can actually hint
or show fetal or placental anomalies and this can actually risk the health of both the mother and the fetus.
Now you always have to do an exam to try to figure out what’s the underlying cause
and the treatment really depends on the severity, the diagnosis,
and the risk of complications whether it’s observation or immediate delivery of the fetus.
Okay, guys, what we’re talking about here are high-yield facts for vaginal bleeding in the third trimester of pregnancy.
Now, what’s important to know is that vaginal bleeding
will actually occur in one out of ten women in their third trimester of pregnancy.
Now, what’s important to remember is that vaginal bleeding is true blood loss from the vagina orifice
but this is different than spotting which is just a few, you know, speckles of blood,
that can happen and that’s considered normal variation to have spotting during pregnancy.
Now, if you do have vaginal bleeding during the third trimester,
this is why this is a board question, it’s important to know, it’s a red flag in your mind.
Now, on the one hand, there are multiple causes to think about for this and it can simply be an unharmful sign of labor,
you know that’s one hint of what we can have.
On the other hand, it can tell you that there are fetal or placental abnormalities in place
and this can cause a substantial risk to either the mother or the fetus.
Now, whenever you see a board question or if you’re out there actually on the wards
and someone’s talking about vaginal bleeding in the third trimester of pregnancy,
you always have to examine the patient and the rationale here is that if it’s a an unharmful sign of labor,
no problem, that’s something that we’re ready for and come planned,
but it could be an anomaly such as a Uterine Rupture, Placental Abruption, Vasa Previa, Placenta Previa,
you know, as we talk about the different causes of third trimester vaginal bleeding,
those are the things we wanna keep an eye out for in the back of our mind, so that’s why examination is always required.
Now, the treatment for vaginal bleeding during the third trimester of pregnancy is really dependant
on what is the complication and the risk of that, and the treatment can go from simple observation if it’s blood loss
and our exam doesn’t show anything, or it can be immediate delivery
if we’re having one of the very dangerous causes of bleeding in the third trimester of pregnancy.