the double decidual reaction, yolk sac, embryo, and cardiac activity with the 5-MI-ta and 9-5-MHz transducers was recorded. The mean sac diameter, embryonic.
Sonography During Early Pregnancy: Dependence of Threshold and DiscriminatoryValues on Transvaginal Transducer Frequency Susan
OBJECTIVE.
E. Rowling1
Our goal at smaller
distinguished
Jill E. Langer Beverly G. Coleman
5-MHz
Harvey
L. Nisenbaum
Steven
C. Horii
with
a higher
9-5-MHz
relative
sac
our ability
diameter
on
Of the 39 pregnancies,
transducer,
a yolk
eight sacs measuring sured 1 1 mm. When found
that
22
(56%)
sac was first seen
all pregnancies
that
had
The ability
dependent
no yolk
the
past
numerous
threshold
of a pregnancy
from
sonographic
sac
sac are the best
Presented atthe annual meeting ofthe American Roentgen Ray Society, Boston, May 1997. 1 All
authors: Department
University
of Radiology,
of Pennsylvania,
Hospital of the
3400 Spruce St., Philadelphia,
PA 19104. Address correspondence to S. E. Rowling. AJR1999;172:983-988
© American
Roentgen
AJR:172, April 1999
would intrauterine
of ectopic
and
enable
diagnosis
normal
Using
the 5-
not definitively yolk seen
sacs were in five of meawe
sac measured
frequency
5.0
imaging.
in early pregnancy
is criti-
and discriminatory
sizes
values
prompt
anembryonic
decreasing
the necessity examinations.
discriminatory
for distinguishing
[I].
the
subsequently
sizes
diagnosis
of
smaller
intrauterine
discriminatory
ofanembryonic
accepted
gestation
a yolk
be present
and
pregnancy
sac sizes [2].
for diagnosis
The
most
widely
values, or sac sizes af-
discriminatory
ter which
of transdetection
and smaller for definitive
and embryo, were determined
sac
yolk
sac or embryo
in normal
should
pregnancy,
always
are 8 mm and
detec-
literature
[2-6].
identified
a number
In addition,
diagnosis
tional
sacs that initially
sizes
larger
fol-
mally plained
normal
from
abnor-
sacs were devised
using
trans-
studies.
nal
from
but
empty
at sac
progressed
nor-
5 to 7.5 MHz,
Unfortunately,
transducer
criteria
appeared
8 mm
study
with gesta-
[7]. These discrepancies are best exby the use of different transducer
frequencies, values, or major
than
a recent
of pregnancies
and excluserial
It was
16 mm, respectively; however, a wide range of discriminatory values has been reported in the
pregnancies, for
sonography
found that the enhanced resolution vaginal sonography enabled earlier
preg-
transvaginal
pregnancy
sonographic
ac-
decidual
possible
by
low-up
mal gestational
cardiac
a double
thereby
criteria, Ray Society
with
sacs.
intrauterine
structures
sonography
nor-
gestational
the earliest
these
of normal sion
normal.
the gestational
Threshold
threshold
to accuintrauterine
for confident
normal
Therefore, of
The original
0361-803X/99/1724-983
within
criteria
of a potentially nancy.
early
of an embryo
or a yolk
tion
with
sac but was
sac and embryo
vesical
of
and discrimina-
and to distinguish
abnormal
Documentation
after revision
or probably
on higher
findings
frequency.
is cur-
sonography
decade,
including
location
pregwith a
gestational sac without a live embryo with I 7 (44%) abnormal pregnancies,
the yolk
transducer
tory values, have been established rately determine the appropriate
May 18, 1998; accepted
a
normal and abnormal pregnancies are smaller on higher frequency than on lower and, therefore, should be redetermined for specific transducer frequencies.
ransvaginal
criteria,
14, 1998.
be
with
and cardiac
in women
gestational
sac by the time
rently the procedure of choice for evaluation of early pregnancy. Over
abnormal reimaged
mm. Using the 9-5-MHz transducer, 4.6-13 mm, and live embryos were
to visualize
on transvaginal
used to distinguish frequency imaging
October
could than
sac, embryo.
frequencies
were normal
in a 6.4-mm
by 13 mm had abnormal
CONCLUSION.
Received
pregnancies transducer
the yolk
at both
8.1-13 mm. The largest normal we compared these pregnancies
mm or no live embryo
T
to visualize
imaging
seen in I 2 gestational sacs measuring 5-13 identified in all gestational sacs measuring
tivity
transvaginal
pregnancies.
RESULTS. MHz
We compared
to mean
and abnormal
mal
and abnormal
frequency
MATERIALS. Thirty-nine patients with potentially a 5-MHz transvaginal transducer were immediately
transducer.
activity
cally
if normal
transducer.
SUBJECTS AND nancies identified with
Peter H. Arger
was to determine
sac sizes
the
frequency
has not been
effect
in the above of transvagi-
on these diagnostic
adequately
addressed.
If
983
Rowling
ability
the
to visualize
the features
of early
pregnancy is dependent not only on the transvaginal approach but also on transducer frethe
quency, values
used
threshold and discriminatory to define a gestational sac as nor-
mal or abnormal
should
The purpose titate
potential
differences
the gestational with
mined
transducers
transducer nancy
at smaller
earlier
menstrual
transducer Subjects
ob-
low
and
to definitively
diag-
intrauterine
preg-
gestational ages
of
images
of relatively
or abnormal
normal
visualization
when
compared. Then we atif a higher frequency
be used
could
was to first quanin
sac contents
high frequency were tempted to determine nose
be reevaluated.
of this study
than
sac sizes when
and thus a 5-MHz
was used. and
A prospective
Methods study
using
transvaginal
sonog-
raphy during early pregnancy was conducted at our sonography suite between January and August 1996. All examinations were performed with sonographic scanners (Advanced Technology Laboratories, Bothell, WA) with a 5-MHz curved transvaginal transducer or a curved 9-5-MHz endocavitary transducer. Criteria for inclusion in the study were a positive urine or serum pregnancy test and an intrauterine gestational sac or fluid collection that did not appear to contain a live embryo on imaging with a 5-MHz transvaginal transducer. Patients with diagnoses of extrauterine gestation and those
et al.
with embryos measuring 10 mm or larger were cxcluded. In accordance with our standard of care at the time of this study, all patients were initially imaged using the 5-MHz probe. In patients who verbally agreed, immediate reexamination of the intrauterine sac or fluid collection was performed
a yolk
using
pregnancies
the 9-5-MHz
endocavitary
transducer
by the
same technologist and sonologist who performed the first examination. The study population consisted of 39 patients who underwent 42 transvaginal examinations (37 patients had one examination, one patient had two examinations,
and
one
patient
had
three
examina-
The patients ranged in age from 16 to 40 years and had indications for pelvic sonography that included exclusion of ectopic pregnancy (n = 18); possible spontaneous abortion or vaginal bleeding (n = 9); assessment of embryo viability (n = 8); pelvic pain (n = 4); establishment of size of embryo and menstrual age (n = 3). Forty-one of the examinations were performed by an experienced technologist and sonologist. An attending radiologist specializing in sonography was present during 20 (48%) examinations, and an abdominal imaging fellow was present during 21 (50%) cxaminations. One (2%) examination was performed by a senior radiology resident. During each examination, the ability of the operators to visualize the double decidual reaction, yolk sac, embryo, and cardiac activity with the 5-MI-ta and 9-5-MHz transducers was recorded. The mean sac diameter, embryonic length, and embryonic heart rate were measured and recorded when possible. The images obtained using each transducer were compared objectively for the presence or absence of tions).
sac, embryo, and heart rate and then compared subjectively for image clarity, confidence in diagnosis, and impact on patient treatment. On the basis of initial and follow-up examinations, patients were subdivided into three groups. Group 1 consisted of patients with normal early in which
sacs
,us sign
984
= not detect , n = visualizea, . with an embryo and cardiac activity documented
ar = equivoca indings. on the initial sonogram or on a follow.up
with
smaller
than
1 3 mm
without
cardiac
activ-
live embryos
were probably normal pregnancies not have confirmatory sonography follow-up at our institution. Group patients
with
bryonic
demise
abnormal
gestations,
and
anembryonic
that
but who did or pathologic 3 consisted of including
em-
pregnancy.
For
this study, anembryonic pregnancy (also known as blighted ovum) was defined as a gestational sac larger than I 3 mm without a yolk sac or embryo. If a yolk nant
sac or tissue was
resembling
identified,
an embryonic
the pregnancy
rem-
was categorized
as embryonic demise. However, in daily practice, embryonic demise and anembryonic pregnancy are often considered synonymous. Results Group I: Normal and CardiacActivity
As shown formed mented
Early Gestation
in Table
with an Embryo
1, examinations
per-
with the 5-MHz transducer docuthe following gestational sac contents
in 16 patients: cardiac
activity
embryo
(n
=
kiedwtd5MHz
aGeations
embryos
ity and yolk sacs were documented on the initial examination or on follow-up sonography. Group 2 consisted of patients with intrauterine gestational
a yolk (n
=
sac and embryo 1); a yolk
7); an equivocal
without
sac without
embryo
without
an a
and 9-541Hz.
sonogram.
AJR:172, April 1999
Sonography
yolk
sac
bryo
(n
6)
(‘1
=
(Fig.
=
I ); an equivocal
1); and
an empty
In comparison,
I).
yolk
sac and em-
gestational
sac
(n
examinations
formed with the 9-S-MHz same I 6 patients showed:
per-
transducer in the a yolk sac and em-
bryo with cardiac activity (n = 5) (Fig. 2); a yolk sac and embryo without cardiac activity (n
=
3); and
sac without
a yolk
8). A double
Because
=
gestational
sac
lengths
was similar
cardiac
activity,
bryo with menstrual
by the
cardiac activity was 8.1 mm (40 days) using the higher frequency a live
transducer,
but
seen until
a mean days) detected
all
gestational
out cardiac
that
normal yolk
documented
transducer
sacs
The largest
detected with the 5-MHz probe was 10 mm. The threshold size for detection of an em-
menstrual
the
Pregnancy
a definite
without
was documented with both transducers.
reaction
Early
was reached. sac
obtained
decidual
on all images
(n
an embryo
days)
strual =
During
embryo
was
sac diameter was
activity
of
reached.
improve 14 (88%)
The
embryo
in a 7.0-mm
sac (39 men-
with-
scoring
of images
of the gestational
sac contents
in 13 (81%) of 16 patients. The diagnosis was actually changed in
(50%)
of 16 patients,
who
had indetermi-
strual days), but an embryo was not typically seen until the mean sac diameter was larger
nate empty
gestational
on imaging
using the lower frequency
transducer,
had definitive
the threshold
the yolk
days).
size
for
the 5-MHz yolk
mean
sac diameter,
than
8 mm
possible
to document
with
the
sac, was 4.6 mm (embryonic
menstrual old
it was
In comparison.
detection
of the
transducer
sac was not typically
ter a mean
sac diameter
age, 37 the thresh-
yolk
was 6.4
sac using
mm,
identified of 7.8 mm
but the until
af-
(39 men-
without
(40
5-MHz
cardiac
gestational Although the 9-5-MHz
menstrual
five
In
a normal
activity
sac, which
was measured
seen
contrast,
tected
embryo
in only
one
6.4 mm.
all eight embryos detected with transducer measured between 2
and 3 mm, cardiac only
days).
transducer,
embryos.
activity The
was documented range
in
of embryonic
sacs or equivocal
normal
yolk
with the higher
findings probe but
sacs or embryos
frequency
probe.
sonography
to confirm
was potentially
eliminated
in five (31%)
embryonic
tively
detected.
ommended
cardiac
activity
Follow-up
but
whom the embryonic
viability patients
was defini-
sonography
not performed
de-
The need
for follow-up because
in
and led to a more confi-
ranged in size from 4.6 to I 3 mm contained yolk sacs on imaging with the 9-5-MHz or size at which
be
of pelvic probe was thought to
of 16 patients
sonographic eight
could
as 2.0 mm.
at the time
physician
clarity
dent diagnosis
9-5-MHz
one normal
as small
the 9-5-MHz
sonography,
and without
activity
of subjective
scanning
not always (45
in an embryo
On the basis
I 3 mm
for those with
and cardiac
was mc-
in one
patient,
in
heart rate was a somewhat
slow 76 beats per minute. Group 2: Probably
Normal
Intrauterine
Gestation
with
Outcome
Unknown
In six (15%) of the 39 patients, no sonographic, pathologic, or clinical follow-up was available (Table
to determine 2). In these
pregnancy
six patients,
outcome the mean
sac
diameter ranged from 3.4 to 13 mm. Examination with the 5-MHz transducer revealed that four sacs appeared empty, one contained a yolk
Fig. 1-21 -year-old woman who tested positive for pregnancy 5 weeks and 1 day after spontaneous abortion in which ectopic pregnancy was suspected. A, Sagittal transvaginal sonogram of uterus obtained at 5 MHz shows intrauterine sac with mean sac diameter of 7 mm. Note double decidual reaction. Yolk sac was not seen. B, Sagittal transvaginal sonogram of uterus obtained at 9-5-MHz (arrow), confirming intrauterine pregnancy.
immediately
afterA
reveals
definitive
yolk sac
an
sac,
equivocal
could
and
one endometrium contained internal fluid collection that
not be distinguished
tational
sac.
transducer mm embryo
Examination revealed with
yolk a yolk
from
a pseudoges-
with
the 9-5-MHz
sacs
in
sac and
three,
a 2-
without
car-
Fig. 2.-34-year-old woman who tested positive for pregnancy and presented with lower abdominal pain. Patient was uncertain of date of last menstruation. A, Sagittal transvaginal sonogram of uterus obtained at 5 MHz shows intrauterine sac with mean diameter of 11 mm and possible ill-defined yolk sac and embryo anteriorly (arrow).
No cardiac
activity
was detected.
B, Sagittal transvaginal sonogram of uterus obtained at 9-5 MHz immediately after A shows substantially improved resolution of gestational sac and yolk sac. C, Coronal transvaginal sonogram of uterus obtained at 9-5 MHz at same time as B reveals 3.0-mm embryo adjacent to yolk sac (between electronic calipers) that had heart rate of 105 beats per minute.
AJR:172, April 1999
985
Rowling
diac
in one, and empty
activity
ual sac signs sacs measuring
in all gestational
seen (37
menstrual
Group
tation 3).
diagnosis was
sacs 4.6 mm
made
Intrauterine
of abnormal in 17 patients
with the 5-MHz the following gestational
yolk
sacs; one equivocal
The
without
9-5-MHz cardiac
sacs, one without
yolk
sacs; one sac containing
bris;
and
four
ges-
(44%)
(Table
The
(five three
the 5-MHz patients
nonspecific
sacs. Three
with de-
of the yolk
large and measured
ap-
in diameter.
obtained
transducer
because
detected (nine
sac); two isolated
with
the
were rated as better than
transducer
transducer resac contents:
a yolk
empty
images
probe activity
yolk
sacs were abnormally proximately 7-8 mm
intrauterine
yolk
sacs.
10 embryos
or larger
seven embryos without cardiac activity with yolk sacs, two without yolk sacs); isolated
six empty
Gestation
Imaging
vealed
decid-
days).
3: Abnormal
The
double
in two patients with gestational 3.4 and 4 mm. A yolk sac was
et al.
clarity
9-5-MHz
those
with
in 12 (71%)
of the 17
of gestational
sac con-
tents was improved, resulting in greater confidence in the diagnosis of embryonic demise or
sac; and
anembryonic
pregnancy.
At the time of the initial nation,
the smallest
ized yolk sac on images obtained MHz transducer and an ultimate anembryonic
pregnancy
strual days).
The diagnosis
nancy
based
was
986
demise
or anembryonic
pregnancy
detected
on the initial
sonogram
or follow-up
exami-
with the 9-5diagnosis of
was 4.7 mm
(37 men-
ofanembryonic
preg-
on the initial
examination
in
one patient with a 13-mm empty sac and was based on lack of normal progression of the pregnancy
on follow-up
sonography
in three
patients. In cases of embryonic demise, normal embryos without cardiac activity in size from mm.
Definitive
-i;tdnedwftIi
aEmb,.,,onic
sonographic
sac that did not have a visual-
2.0 to 7.1 mm, with diagnosis
a mean
of embryonic
541Hz
other the abranged of 4.1 demise
and 9441Hz
sonogram.
AJR:172, April 1999
Sonography was based
on initial examinations
that showed
an
During
values: from 6 to 13 mm for documentation
confusing,
5-MHz
standardization
The diagnosis
based
on the presence
larged
yolk sac, thickened growth
bryonic
ofdemise
was also
of sac distortion, amnion,
on follow-up
an en-
or lack of em-
pelvic sonography.
Over the past decade, phy has proved phy
superior
for the evaluation
pregnancies.
lished
one feasible
in these
Transducer
studies.
from
S to 7.5 MHz,
sizes
were
considered
as a variable
to transvesical
sonogra-
pregnancy
sonograms
have
sac sizes at which
gestational
published
first trimester
studies
estab-
the yolk sac
frequency
on
resolution
seen with higher
sizes are commonly
practice to distinguish tions from anembtyonic threshold
used
in daily
normal
potentially pregnancies.
sizes have become
sac
tant because
smaller
threshold
gesta-
However,
equally sizes
impor-
enable
the
bryo, quency. ages
4 mm,
pregnancy, obtained
and cardiac
and 8 mm,
respectively menstrual
transvaginal a 5-MHz
and
serial quantitative
dotropin
levels
obtained
for a normal
and
pelvic
are
[8]. Howweek
sonographic transducer
with
equivocal,
activity
sonograms
or abnormal
of
findings are often
human
gonamust
be
sac and embryo
are 8 mm and
16
mm, respectively, but at these sizes the diagnosis of abnormal pregnancy is not always accurate and may potentially
lead to erroneous
ofpregnancy failure yields a wide range
[71. Scrutiny ofthe literature
Fig. 3.-31-year-old
of suggested
diagnosis
discriminatory
to the
imaging.
activity
is dependent The 9-5-MHz
that were
the 5-MHz
by on
transducer
superior
to those
transducer
in all three
helpful
confirm 16
the presence
gestational
agnosis
of
transvaginal
transducer produced obtained patient
in evaluation
sacs and thereby pregnancy
topic
a live embryo which
allowed
the di-
pregnancy
and anembryonic
of both
ec-
pregnancy
at
the time of the initial sonogram. In contrast, eight (50%) of the 16 sacs appeared empty or had equivocal
findings
on images
obtained
the S-MHz transducer, which would have creased the necessity for serial follow-up. In four (18%) of 22 patients possibly normal early gestations
with in-
with
sac
because
contents.
also gesta-
of improved
or
a 5-mm
allow-
documentation
For
embryo
example,
could
in
be seen
the 9-5-MHz transducer, diagnosis was definitive
demise.
embryo
was
of the embryo,
measurement
clearly only with and the sonographic
In another
without
measurable
cardiac
at higher
patient, activity
frequency,
a was and
thus demise was suspected (Fig. 3). Our data show that use of a higher frequency transducer could help exclude ectopic pregnancy and help diagnose both normal and abnormal
pregnancies
diameters
at
and earlier
our patient tients,
smaller
menstrual
population
mean ages.
was small
not be established could not determine
we
criminatory
values to be used
a 9-5-MHz
transducer.
esting
trends
were
noted
that
and ultimate in several accurate
for imaging
However, will
sac
Because padiswith
a few interneed
larger
future studies for confirmation. The threshold and discriminatory sac size for detection of the yolk sac with the 9-5-MHz mm (5 mm if rounded
transducer were both to the closest whole
4.6
number)
with normal or in group I or
a
avoided
again
of abnormal
outcome could
at menstrual 16
exclusion
was
them
transducer
particularly
of abnormal
only
could be seen as early as
enabled
frequency
accurate
im-
of nor-
In
which
after
pregnancy
by imaging
in imaging
for embryonic
groups
agesaslowas37days.Infive(3l%)ofthe patients,
ing
4.3-mm
with
probe. discrimina-
of 8 mm
and delineation
clarity
fre-
of at least a yolk sac in all
intrauterine
higher
one patient,
mal early pregnancies. In group 1, scanning with the 9-5-MHz transducer allowed us to
40 days,
intrauterine
gestation or ectopic pregnancy to be diagnosed. The most widely accepted discriminatory sizes for the yolk
cardiac
The
sacs,
close
quoted
transducer.
tional
that they should be better
frequency
but was particularly
for detection
sizes
the seventh
8 mm,
ever, before
sac
and
sonography
gestation
The reported threshold of the yolk sac, embryo,
thin, and usually
the 9-5-MHz
tissue sac
measuring
frequency
widely
of abnormal patients
helpful
and
the
sac diameter
often
gestational
sacs
obtained with the 5the yolk sacs were
yolk sac must be seen in a normal pregnancy would have been exceeded. The potential mis-
of trans-
The results ofthis study confirm the hypothesis that the ability to visualize the yolk sac, em-
distinction
of a potentially normal intrauterine from a pseudogestational sac of ecpregnancy at an earlier menstrual age.
of wide-
despite effects
the earliest
it is logical
transducer,
clinical
values,
ducer
natory
tory mean
in these
in implementation
not be definitively
gestational
seen with the higher patients,
diagnosis
general
are small,
be seen
MHz clearly
of early
ofthe
contents
may
or
sacs could
within
or larger on images probe, even though
8 mm
these
in studies
in interpretation
discriminatory
(threshold sizes) or must be seen (discriminatory sizes) in normal pregnancies [2-6, 81. Discrimi-
activity
ranged
2, yolk
group
documented
transducers. Nonethehas not routinely been
knowledge Because
cardiac
used
discriminatory
reported
spread
definition.
with
is the lack of transducers
and smaller
sonogra-
of early
of a
frequencies
more commonly
transvaginal
Numerous
or embryo
topic
explanation
of transvaginal
that used higher frequency less, transducer frequency
Discussion
Pregnancy
yolk sac and from 9 to 18 mm for a live embryo [2-6]. Although these inconsistencies are at first
embryo without cardiac activity that measured S mm or larger in three patients with the 9-5-MHz probe and in two of these three patients with the probe.
Early
because a yolk sac was seen in all nor-
mal gestations was not seen
measuring in two
4.6 mm or larger normal sacs
possibly
and that
woman who was 7 weeks 4 days pregnant based on last menstruation. Patient presented with vaginal bleeding.
A. Sagittal transvaginal sonogram of uterus obtained at 5 MHz shows intrauterine sac with
mean sac diameter
of 6.9 mm and possible
yolk sac.
B, Sagittal transvaginal sonogram of uterus obtained at 9-5 MHz immediately after A shows 4.3-mm embryo rather than yolk sac. Diagnosis is changed from potentially normal intrauterine
pregnancy
AJR:172, April 1999
to suspected
embryonic
demise.
987
Rowling
measured 3 and 4 mm. This value is similar to the reported threshold value of4 mm for potential detection
of the yolk
smaller
the previously
than
sac, but substantially reported
detectable
of
2-3
natory sizes for yolk sac detection of8-l3 mm. Although the threshold sac size for detec-
days.
Taking
error
inherent
tion
rump
of the
ducer
yolk
was
with
seen
the
the yolk
mm,
6.4
consistently
sac
at a mean
5-MHz
trans-
sac was
more
sac diameter
of 8
activity.
Pulsatile
contrac-
begin in the primitive heart on menday 38 or 39 [8], and an embryonic
tions strual length
discrimi-
cardiac
et al.
mm into
corresponds
consideration
of the crown-
Therefore,
absence
were
may
actually
higher
be
frequency
larger
than
was
often
measurement
cavity
artifact
and the diminished
with
higher
embryonic cal because
frequency
and
sonography
before
embryos measuring transvaginally [9], detection ent. With
menstrual
days)
and
however, that seen in normal
a live
and
for
seven (88%) of eight normal 8-13 mm. Because an embryo pregnancy
was
seen
in
sacs measuring was not seen in sac diameter
all pregnancies
without of 13 mm tentatively
live embryos at mean sac diameter or larger were abnormal, we may that if a live embryo
is not detected
by a mean sac diameter of 13 mm, the pregnancy is abnormal. However, in the 16 patients with
normal
pregnancies,
sac that measured and we therefore
only
discriminatory
eight
seen
All
988
embryos
was found,
not determine
racy of this potential sured between
one gestational
13 mm or larger could
2 and 3 mm,
the accuvalue.
in group
1 mea-
only
five had
yet
all embryos
definition
or larger
ac-
measurement
accepted,
of demise
S mm
cardiac
is
more con-
as an embryo
to characterize
an early
or abnormal
is criti-
without
cardiac
ac-
sac, embryo,
can be documented
and cardiac
within
smaller
activity
gestational
using
therefore at earlier menstrual the higher frequency transducer.
fore,
the
sacs,
ages, There-
and
threshold
for currently
and
discriminatory
in clinical
routinely used early gestational
sacs
available
practice
should
be
higher
frequency
ducers
and clearly reported in the literature.
cific
sizes
to assess
redetermined
trans-
as frequency-spe-
tivity on transvaginal sonography [9]. Because no embryos in our study measured between 3 and 4 mm, cance
we could
of lack
not determine
of cardiac
could
during
transducer
on the ba-
alone.
We acknowledge
our current
in
our
data. Our study
were assumed nancies because
fellows their
appropri-
it was
1 . Nyberg
by
and unknown patients who
to have normal a live embryo
In addition,
patients
direct
were
comparison
included
early had
pregbeen
not
deter-
in our study
of image
Although
quality
for
obtained
are currently
manufacturers
use 5-MHz
transducers.
field of view
limited
favor-
Because
and poorer
tissue
of the penetra-
tion, a higher frequency transducer can be inadequate for evaluation of myomatous uteri or ovaries that are positioned cephalad or laterally. A multifrequency transducer that allows manual selection
ofa range
of optimal depth of fine detail. This ning
offrequencies,
may prove to be ideal
MHz,
study
protocol.
from S to 7.5 for a combination
of penetration
has influenced If a patient
the first 6 menstrual
in acquiring
weeks
the
for
data
neces-
of this study.
and resolution our current
is clinically of pregnancy
scanwithin and
DA, Laing
abortion:
sonographic
abnormal
gestation
397-400 2. Levi CS,
Lyons
of nonviable
FC, Filly
RA. Threatened
distinction
sacs.
EA, Lindsay
pregnancy
of normal
Radiology
with
and
1996;158:
Di. Early endovaginal
diagnosis US. Ra-
1988;l67:383-385 3. Bree RL, Edwards M, Btihm-V#{233}lez M, Beyler diology
5,
Roberts J, Mendelson EB. Transvaginal sonography in the evaluation of normal early pregnancy: correlation with HCG level. AiR 1989;153:75-79 4. de Crespingy
LC.
Early
diagnosis
failure with transvaginal ultrasound. Gynecol 1988;l59:408-409 5. Cacciatore B, Titinen A, Stenman P.
ing production of higher frequency transvaginal transducers, many institutions continue to routimely
to the
imaging
References
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is also limited
population in some
body
of Pennsylvania
at the University diligence
our thanks and
design.
was
mined whether the six patients in group 2 had normal or abnormal pregnancies, but these
like to express technologists
the 5-MHz
study
a live embryo
the small patient ultimate outcome
We would sonography
sary for completion a bias against
inherent
in which
Acknowledgments
this
Therefore, a of embryonic
not be recommended
sis of this study
Cases
the signifi-
activity
with the two transducers. were
at a mean
of 1 1 mm and because
servative measuring
documented.
embryo mm (39
embryo
days). 2-3 mm
This
of
than 3 stage of
ately seen with the lower frequency ducer were not reviewed or compared
of cardiac
a normal was 7.0
for
8.1 mm (40 menstrual Embryos measuring
one normal
identito be
activity may be differtransducer, the thresh-
for documenting cardiac activity
nonviable.
than the currently
demise
of an embryo
of cardiac a 9-5-MHz
population,
that did not have
reverber-
between 1 and 3.9 mm and therefore expected
sac sizes for detection
smaller
patient
3 mm
imaging.
transvesical
development
In our small
brief phase of development. change in the current definition
been small
on
measured
activity. It has been shown, cardiac activity is not always
conclude
using can be of the
and discriminatory of an embryo and
cardiac activity have an embryo is too
seen
the
slightly
obtained
Historically, threshold sizes for documentation
old size without
13 mm. using
transducer. This difference by the clearer delineation
chorionic
clearly
than
as measured
probe
the
the S-MHz explained ation
larger
sac diameter
ability
sac as normal
that the yolk
transducer.
tivity
The mean
the
gestational
transducer. the hypoth-
9-5-MHz
than
ducer
that
esis
frequency
our data confirm
cally dependent on the frequency of the transvaginal transducer used. Our data also show
larger
size for detecthe 5-MHz trans-
a higher
length, heart motion can likely be detected soon after it develops when using the
gestational sac measuring clearly seen on higher Therefore, the discriminatory tion of the yolk sac with
using
scan
In conclusion, of
the range
in measurement
cardiac activity in embryos smaller mm most likely represents a normal embryologic development.
but was imaging.
tially
to 40-41
mm or larger and not always seen until a discriminatory size of 13 mm in group 1. In one patient from group 2, a yolk sac could not be visualized with the 5-MHz transducer in a 13 mm frequency
the uterus appears normal in size on preliminary transabdominal images, we preferen-
6.
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vaginal
ultrasonography
naecol
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Goldstein early
RB.
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U-H,
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Ylostalo
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St.
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9. Levi CS, Lyons EA, Zheng nal ultrasound: demonstration
XA, et al. Endovagiof cardiac activity
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AJR:172, April 1999
