00:01
So moving on to that ultrasound
and establishing
the gestational age.
00:06
Again using ultrasound the 1st trimester
is the most accurate.
00:10
How we use it?
We measure the crown-rump
length.
00:13
So the distance from the crown
of the fetus to the rump.
00:16
We expect that to be within
one week of the last menstrual
period.
00:21
So let me explain that
in a little bit detail.
00:23
If by a patient's last menstrual
period,
the fetus is measuring 8 weeks
and 2 days.
00:29
And by our ultrasound,
the measurement is 6 weeks
and 5 days.
00:34
We would refer to
the ultrasound.
00:37
Last menstrual period again is
only accurate if it's a 28 day
cycle and it's regular.
00:43
The ultrasound is only going
to tell us how far along
the pregnancy is based on
the date of conception.
00:49
So in that case we will go
with the gestational age
the ultrasound is giving us.
00:53
Let me give you another example.
00:55
If the last menstrual period
says the patient is 7 weeks
and 2 days, and our ultrasound
says she's 7 weeks and 5 days,
which one would we choose.
01:05
You guessed it right.
01:06
We would use the last
menstrual period.
01:08
Because the last menstrual
period in the ultrasound are
within one week of each other.
01:14
Now, in the 2nd and 3rd
trimester, we can still use
that for establishing
gestational age.
01:19
But it is not quite as accurate
as we do in the 1st trimester.
01:21
In the 2nd and 3rd trimester
we use the biparietal diameter
which is the distance between
the parietal bones in the head.
01:30
We use the abdominal
circumference.
01:32
And we use the femur length to
determine the gestational age.
01:34
Now here is a little rule.
01:36
In the first trimester,
the ultrasound can be off
by one week.
01:39
2nd trimester two weeks,
third trimester three weeks.
01:44
So why the big difference.
01:45
Why does it increase as
a gestational age increases.
01:48
Well there are many things
that influence the size
of the fetus as we get into
2nd and 3rd trimester.
01:53
Their fetal factors,
their maternal factors,
their placental factors.
01:58
Again as we discussed in the 1st
trimester, the only thing that
influences the gestational
age is the date of conception.
02:07
So let's move to
another question.
02:10
A 23 year old presents
to the emergency room
with complaint of left
lower quadrant pain.
02:14
She states that the pain
is 3 out of 10.
02:18
She states she has
slight vaginal bleeding.
02:20
And she reports a positive
pregnancy test approximately
6 weeks ago.
02:24
This is her first pregnancy.
02:26
She has no other medical
problems or surgical history.
02:29
On physical exam, vital signs
are stable and she is afebrile.
02:33
On sterile speculum exam, you
see slight vaginal bleeding.
02:37
And then by manual exam,
she has slight tenderness
in the left lower quadrant.
02:41
Lab result show that her
beta-hcg is 400 milligrams
per decaliter.
02:46
On the transvaginal ultrasound,
there is no gestational sac
in the uterus, there is no
free fluid in the pelvis.
02:52
And the adnexa are within
normal limits.
02:55
So what is the next best
step in her management?
A. Admit the patient to
the hospital and prepare her
for surgery.
03:03
B. Reassure the patient that her pregnancy is normal
and her pain is expected for
her gestational age.
03:08
C. Proceed with medical management
as patient most
likely has an ectopic pregnancy.
03:13
or D. Repeat the beta-hcg
and ultrasound in 48 hours.
03:17
The answer for this one is D.
03:19
Remember that we don't see
anything on transvaginal
ultrasound in the uterus,
until the beta-hcg is at least 2000.
03:27
With this patient her
beta-hcg was only 400.
03:30
So this may very well
be a normal pregnancy.
03:32
However, may be an
ectopic pregnancy.
03:35
We really just don't have
enough information to tell.
03:37
So the correct answer is to
repeat the beta-hcg in 48 hours.
03:41
Because we do expect
it to rise by 50%
if this is a normal pregnancy.
03:45
And then repeat the ultrasound.
03:47
Because we may be able to see
something in the uterus
by that time.
03:52
So just to recap.
03:54
This is the high-yield
information that you need
to know for this lecture.
03:57
Confirming pregnancy
and establishing
gestational age.
04:00
Pregnancy can be established
by last menstrual period.
04:03
Urine or serum pregnancy
test or ultrasound.
04:06
The last menstrual period is
the most accurate for
establishing gestational age
if it's consistent with
the transvaginal ultrasound.
04:14
If the last menstrual period
is unknown, 1st trimester
ultrasound is the most
accurate way to establish
the gestational age.
04:22
When the beta-hcg is greater
than 2000 milligrams per
decaliter, gestational sac
should be seen on ultrasound.
04:29
And then remember that other
little fact I told you.
04:32
In the 1st trimester,
the ultrasound should be within
one week of the last
menstrual period.
04:36
In the 2nd trimester, two weeks.
04:38
And in the 3rd trimester,
three weeks.