Let's now talk about confirming and dating pregnancy.
So here's a case.
A 19 year old presents to the emergency room with
complaint of nausea,vomiting and right lower quadrant pain.
She states the pain has becoming increasingly worse over the last
12 hours.
She has no medical problems and no surgical history.
She has never been pregnant.
Her last menstrual period was 10 weeks ago.
But she reports cycles are irregular.
On physical exam her vital signs are stable and she is afebrile.
She is tender in the right lower quadrant on abdominal exam.
On pelvic exam, there is no cervical motion tenderness
but she has fullness and tenderness
in the lower right quadrant.
What is the next best step in her management?
A. Ultrasound
B. Urinary analysis.
C. Urine pregnancy test.
or D. Serum pregnancy test.
Let's go through the lecture to figure out what the answer is.
So there are several ways that we can confirm pregnancy
and we can establish gestational age.
We're going to talk about each of these and talk about
the risks and the benefits and why one test is better
than the other.
So first of all let's talk about last menstrual period.
If we know a patient's last menstrual period and cycles
are regular, we can't determine the gestational age.
And we use something called Naegele's rule.
So what we do is we take the last menstrual period
subtract 3 months and we add 7 days.
So if a patient tells us
her last menstrual period is April 1st,
we subtract 3 months, giving as January at 7 days
giving as the 8th.
And we would know that her due date is January the 8th.
Okay, again this is based on an accurate last menstrual period.
We can also confirm pregnancy through a urine pregnancy test.
Now the urine pregnancy test is a qualitative test.
That means that it either tells that the patient is pregnant
or the patient is not pregnant.
So there are some benefits to that and that we can tell
the patient such is in our case that we discuss when we're
trying to figure out what may be a differential diagnosis.
But this does not tell us how far along the pregnancy is.
Next is the serum pregnancy test.
Now this is a quantitative test.
So this tells us exactly how much beta-hcg is in the blood.
Different than the urine pregnancy test if we remember,
that one is qualitative so just as the patient is pregnant
or the patient is not pregnant.
With that serum test,
because we can determine the amount of hcg,
we can use that to help us with our ultrasound to determine
if we should or should not see something in the uterus to help
establish gestational age.
When the beta-hcg is at least 2000,
we should see something in the uterus on
transvaginal ultrasound.
When the beta-hcg is 6000, we should be able to see something
in the uterus on abdominal ultrasound.
Speaking of ultrasound this is the most accurate way to
determine the gestational age.
We expect with ultrasound in the 1st trimester that
when we measure the fetus from the crown-rump length
that it will be within one week of the last menstrual period.
We'll talk about that in a little bit more detail
as we go throughout this slide.
This is a high yield amount of information remembering how we
confirm pregnancy and establish the gestational age
using these 4 tests.
So back to our patient.
She's A 19 year old presents in an emergency room.
Again complaining of nausea, vomiting and right lower
quadrant pain.
And last menstrual period was about 10 weeks ago.
And on exam we felt some fullness on the right.
Now when we again think about these options of what
we should do next.
What do you think the answer is?
The answer is D.
We want to do a serum pregnancy test.
Remember that with the urine pregnancy test
this is qualitative.
So this just tells that the patient is pregnant
or if the patient is not pregnant.
That serum pregnancy test is more important
because it actually tells what the beta-hcg is.
So that when we do our ultrasound, we'll know if we
should see something in the uterus or if it's too early.
That helps with our differential diagnosis.