Early pregnancy assessment with transvaginal ultrasound scanning.
ABSTRACT To establish normal parameters in early pregnancy through transvaginal ultrasonography so that gestational age can be determined and to correlate the sonographic findings with serum human chorionic gonadotropin (hCG) levels calibrated against the first international reference preparation standard.
Thirty-five women with normal intrauterine pregnancy.
Serial measurement of the serum hCG level and the diameter of the gestational sac through transvaginal ultrasonography.
The gestational sac could not be visualized when the hCG level was less than 1100 IU/L. The average growth rate of the sac was 0.9 mm/d. The threshold values for sac diameter, serum hCG level and gestational age below which the yolk sac was not visible were 3.7 mm, 1900 IU/L and 36 days respectively; the corresponding values above which the yolk sac was always visible were 6.7 mm, 5800 IU/L and 40 days. The threshold values below which cardiac activity was not visible were 8.3 mm, 9200 IU/L and 41 days respectively, and the corresponding values above which cardiac activity was always visible were 14.0 mm, 24,000 IU/L and 46 days. The mean gestational ages and the 95% confidence and prediction intervals were tabulated so that measurement of the gestational sac diameter could be used to estimate gestational age early in normal pregnancy.
Transvaginal ultrasonography enables detection of an intrauterine sac and reliable estimation of gestational age on the basis of sac dimensions before an embryo can be seen.
- SourceAvailable from: Moawia Bushra Gameraddin[Show abstract] [Hide abstract]
ABSTRACT: Correct assessment of gestational age is a cornerstone of management of any obstetric case. Several anatomical parameters are useful in the assessment of gestational age. The ultimate aim of this study is to determine the fetal gestational age through the measurement of the foot(foot length) and to determine the accuracy of fetal foot length in estimating gestational age. Methods: There were one hundred pregnant ladies in 2nd and 3rd trimesters had been selected randomly in different medical centers and hospitals in Khartoum State. They were scanned with ultrasound using the international protocols and guidelines of obstetric ultrasonography. Statistical analysis using regression equation and correlation was obtained. Results: There was a strong correlation between fetal foot length and gestaional age. Conclusion: Fetal foot length is a reliable parameter for use in the assessment of gestational age and is particularly useful when other parameters do not accurately predict gestational age. The study derived an important equation to estimate the GA, the GA= 82.411+2.191FtL. [Moawia Gameraddin, Suliman Salih, Mohamed yousef. Evaluation of Gestational Age with Fetal Foot Length Using Ultrasonography. J Am Sci 2014;10(1):5-7]. (ISSN:Journal of American Science. 01/2014; 10.
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ABSTRACT: A review of literature and current practice of normal fetal growth assessment is presented. Ultrasonographic dating of pregnancy in the first, second, and third trimester is reviewed. Individual biometric parameters are examined, and the proper use of the fetal growth profile is explained. Use of this information is discussed as it pertains to the single pregnancy.Journal of Diagnostic Medical Sonography 01/1995; 11(4):176-187.
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ABSTRACT: Transvaginal sonogram (TVS) is now the gold standard for the evaluation of infertility and assisted reproduction, early pregnancy, ectopic pregnancy, and first trimester pregnancy-related abnormalities. Additionally, identification of fetal abnormalities is also performed via TVS. The primary advantage of TVS over transabdominal sonography lies in its ability to place a high-frequency transducer next to the regions of interest. This chapter reviews the methodology and applications of transvaginal ultrasound usage in the practice of reproductive medicine, including its use in conjunction with in vitro fertilization. Specific guidelines are presented for optimal use of transvaginal ultrasound.
Early pregnancy assessment
with transvaginal ultrasound scanning
Salim Daya,* MB, MSc; Sheila Woods,t MD; Susan Ward,* RN;
Ray Lappalainen,t RDMS; Chris Caco,t MD
Objective: To establish normal parameters in early pregnancy through transvaginal
ultrasonography so that gestational age can be determined and to correlate the
sonographic findings with serum human chorionic gonadotropin (hCG) levels calibrated
against the first international reference preparation standard.
Patients: Thirty-five women with normal intrauterine pregnancy.
Interventions: 'Serial measurement of the serum hCG level and the diameter of the
gestational sac through transvaginal ultrasonography.
Main results: The gestational sac could not be visualized when the hCG level was less
than 1100 IU/L. The average growth rate ofthe sac was 0.9 mm/d. The threshold values
for sac diameter, serum hCG level and gestational age below which the yolk sac was not
visible were 3.7 mm, 1900 IU/L and 36 days respectively; the corresponding values
above which the yolk sac was always visible were 6.7 mm, 5800 IU/L and' 40 days. The
threshold values below which cardiac activity was not visible were 8.3 mm, 9200 IU/L
and 41 days respectively, and the corresponding values above which cardiac activity was
always visible were 14.0 mm, 24 000 IU/L and 46 days. The mean gestational ages and
the 95% confidence and prediction intervals were tabulated so that measurement of the
gestational sac diameter could be used to estimate gestational age early in normal
Conclusions: Transvaginal ultrasonography enables detection of an intrauterine sac and
reliable estimation 'of gestational age on the basis of sac dimensions before an embryo
can be seen.
Objectif: ktablir, par ultrasonographie transvaginale, les mesures normales au debut de
la grossesse afin de pouvoir determiner l'age gestationnel et etablir un lien entre les
constatations sonographiques et les niveaux seriques de gonadotrophine chorionique
humaine (GCH) etalonnes en fonction du premier etalon international de preparation
Coptexte: Clinique de traitement de l'infertilite.
Patients: Trente-cinq femmes en etat degrossesseintrauterine normale.
Interventions: Ser,ie de mesures du niveau serique de GCH et, par ultrasonographie
transvaginale, du diametre du sac gestationnel.
Resultats principaux : On ne pouvait visualiser le sac gestationnel lorsque le niveau de
GCH etait inferieur a 1 100 UI/L. Le taux de croissance moyen du sac etait de 0,9
mm/j. Les valeurs minimales du diametre du sac, du niveau serique GCH 'et de l'age
gestationnel au-dessous desquelles la vesicule vitelline etait invisible etaient respective-
ment de 3,7 mm,
desquelles la vesicule vitelline
jours. Les valeurs minimales au-dessous desquelles l'activite cardiaque n'etait pas visible
etaient respectivement de 8,3 mm, 9 200 UI/L et 41 jours, et les valeurs correspondantes
1 900 UI/L et 36 jours. Les valeurs correspondantes au-dessus
etait toujours visible etaient de 6,7 mm, 5 800 UI/L et 40
From the departments of*Obstetrics and Gynaecology and tRadiology, McMaster University, Hamilton, Ont.
Dr. Daya is a career scientist ofthe Ontario Ministry ofHealth.
Reprint requests to: Dr. Salim Daya, Department ofObstetrics and Gynaecology, McMaster University, 1200 Main St. W, Hamilton, ON
CAN MED ASSOC J 1991; 144 (4)
au-dessus desquelles l'activite cardiaque etait toujours visible etaient de 14,0 mm,
24 000 UI/L et 46 jours. On a etabli le tableau des ages gestationnels moyens et des
intervalles de prediction et de confiance a 95 % afin de pouvoir utiliser le diametre du
sac gestationnel pour evaluer l'age gestationnel t6t au cours d'une grossesse normale.
Conclusion: L'ultrasonographie transvaginale permet de detecter la presence d'un sac
intrauterin et d'effectuer une estimation fiable de l'age gestationnel en fonction des
dimensions du sac avant que l'embryon ne devienne visible.
Ultrasonography is an important tool in the
assessment of pregnancy, and its use in
clinical diagnosis has increased dramatically
with improvements in imaging technology. The re-
cent development of transvaginal ultrasonography
has resulted in better images because of the place-
ment of higher frequency transducers closer to the
pelvic organs. This technique has enabled the detec-
tion of intrauterine pregnancy earlier than with the
transabdominal approach and has become particu-
larly useful in the evaluation of ectopic and other
abnormal pregnancies. '
The use of radioimmunoassay for human chori-
onic gonadotropin (hCG) has also allowed early
detection of pregnancy. Several attempts have been
made to correlate the ultrasonographic appearances
of early intrauterine pregnancy with simultaneous
quantitative measurements of hCG so that normal
pregnancies can be distinguished from abnormal
ones.2'3 These correlations have led to the definition
of an hCG discriminatory zone, above which an
intrauterine gestational sac could be detected. With
the use of transabdominal scanning this zone was
found to represent serum hCG levels of 6000 to
6500 1U/L.2 The improved sensitivity of transvaginal
Since hCG has not been completely character-
radioimmunoassay kits must be calibrated against an
agreed-upon standard. In 1975 the World Health
Organization established the first international refer-
ence preparation (1st IRP) ofhCG for immunoassay
and recommended that it be used to calibrate all
commercial hCG kits.4 Unfortunately not all kit
relatively impure and heterogeneous second interna-
tional standard (2nd IS) for hCG bioassay, estab-
lished in 1964.5 This has significant implications for
physicians relying on quantitative hCG determina-
tions to aid in clinical diagnosis. To compare the
2nd IS with the purer 1st IRP standard a conversion
factor has been suggested:
fl-hCG = 2.2 IU/L of the 1st IRP.6 However, in an
analysis of 10 different commercial kits Rasor,
Farber and Braunstein7 found that the serum hCG
values determined with kits calibrated against the 1st
IRP standard were 1.75 to 3.5 times higher than
re-evaluation of the
all commercially available hCG
still calibrate their kits against the older,
1 IU/L of the 2nd IS
those determined with kits calibrated against the 2nd
conversion factor unless the two standards are used
in the same assay-a technique that is not practi-
cal.8 Consequently, when relying on hCG quantita-
tion for decision-making one must be aware of the
standard used for calibration in the laboratory where
the test was done.
We performed this study (a) to evaluate the use
of transvaginal ultrasonography in early pregnancy
in order to establish normal parameters for gesta-
tional age assessment by measuring gestational sac
diameters and (b) to correlate the sonographic ap-
pearance of early embryonic structures with serum
hCG levels determined with kits calibrated against
cently been reported in which the serum hCG
levels were determined with kits calibrated against
the 2nd IS.6'9
itis not meaningful to use a single
1st IRP standard. Similar studies have
Thirty-five women who conceived as a result of
McMaster Hospitals, Hamilton, Ont., participated in
the study. All had singleton intrauterine pregnancies
that progressed beyond 20 weeks' gestation. The
pregnancies were confirmed through serum hCG
testing, and their progress was monitored by serial
hCG measurements performed every 2 to 7 days (3
to 4 days on average) until about 60 days' gestation
and by transvaginal ultrasound scanning every 1 to 2
weeks until 8 weeks' gestation. Quantitation of hCG
was performed by means of radioimmunoassay di-
rected against the ,B subunit of the molecule and
calibrated against the 1st IRP standard.'0
Gestational age was determined by each of two
methods. Menstrual gestational age was calculated
from the first day of the last menstrual period. True
(corrected) gestational age was calculated with the
use of the normal curve for hCG production in early
pregnancy.'0 The natural logarithm of the hCG level
was plotted against the gestational age, and the
resulting curve was compared with the normal curve.
The assumption underlying the use of the normal
curve was that ovulation occurred on day 14 of a
28-day menstrual cycle. The validity of this assump-
tion has been confirmed in patients achieving preg-
nancy through in-vitro fertilization, in which oocyte
CAN MED ASSOC J 1991; 144 (4)
retrieval was retrospectively assigned as being on day
14 of gestation."" I2 Thus, the normal curve repre-
sents hCG production during the early stages of an
ideal gestational period of 280 days. If the patient's
hCG curve fell to the right ofthe normal curve, then
ovulation was assumed to have occurred after day
14, and the average number of days between these
two curves was subtracted from the menstrual gesta-
tional age. Similarly, if the curve fell to the left, then
ovulation was assumed to have occurred before day
14, and the relevant number of days was added to
the menstrual gestational age. Using pregnancy data
from in-vitro fertilization treatment we found that
the mean difference between the actual gestational
age and that expected from the normal curve was
0.44 (standard deviation [SD] 0.43) days, 84% of the
data points falling within
observations indicate that the normal curve is very
precise for calculating gestational age.
All ultrasound measurements were performed
transvaginally with the use of an Aloka SSD-650
machine fitted with a 5-MHz convex sector probe
with a 600 scanning angle, 0.5-mm axial resolution
and 1.7-mm lateral resolution (Omnium Medical
Devices of Canada Inc., Richmond Hill, Ont.). The
mean diameter of the gestational sac was calculated
on the basis of measurements of the inner sac wall in
three planes at right angles to each other. The sac
was thoroughly scanned to identify a yolk sac and a
fetal pole; when the latter was identified much effort
was taken to determine whether cardiac activity was
day of the curve.'2 These
The relation between gestational age and mean
sac diameter was explored through regression analy-
sis. Student's t-test was used to determine whether
the slopes of the regression lines were significantly
different from zero. We identified cutoff points for
mean sac diameter, true gestational age and serum
hCG levels below which embryonic characteristics
were not visible on ultrasonography and above
which they were always visible.
Data from 113 ultrasound measurements were
evaluated along with the corresponding serum hCG
levels. In five cases the gestational sac was not
visualized when the hCG level was less than 1100
IU/L; the mean hCG level was 650 (SD 356) IU/L
(extremes 214 and 1091 IU/L). Above this threshold
level the gestational sac was always visualized. Table
1 shows the cutoffpoints for mean sac diameter, true
gestational age and serum hCG level below which a
yolk sac and cardiac activity were not identified and
above which they were always present.
We found a linear relation between true gesta-
tional age and mean sac diameter (r = 0.95, p <
0.0001) and between menstrual gestational age and
mean sac diameter (r = 0.77, p < 0.0001) (Figs.
and 2). Since the correlation coefficient was much
better with true gestational age than with menstrual
gestational age all further inferences were made with
the use of the true gestational age regression model.
Fig. 1: Relation between mean diameter of gestational sac
and true gestational age. Equation for regression line (solid
line) was as follows: gestational age (in days) = 0.882(mean
sac diameter[in millimetres])+ 33.117. Dotted lines repre-
sent upper and lower limits of95% prediction interval (PI).
CAN MED ASSOC J 1991; 144 (4)443
Mean sac diameter, mm
Table 1: Discriminatory measurements in early pregnancy with respect to
visualization of embryonic characteristics by transvaginal ultrasonography*
*For each parameter the discriminatory measurements are values below which the characteristics
were not visible (N) and above which they were always present (P).
thCG=human chorionic gonadotropin.
The slope of the regression line was significantly
different from zero (t = 38.52 with 111 degrees of
freedom, p < 0.0001), and there was no significant
Fig. 2: Relation between mean diameter of gestati
and menstrual gestational age. Equation for regres:
(solid line) was as follows: gestational age (in
0.821(mean sac diameter[in millimetresi) + 35.081
lines represent upper and lower limits of95% PI.
;l iar.- etc.
lack of fit ofthe model to the data (p = 0.207).
In early pregnancy the rate of growth of the
gestational sac was about 0.9 mm/d. Using the
regression equation gestational age
0.882(mean sac diameter [in millimetres]) + 33.117
we calculated the gestational age for various mean
sac diameters (Table 2). The 95% confidence interval
(CI) for the mean gestational age and the 95%
prediction interval (PI) for the observed gestational
age were also calculated (Table 2, Fig. 3).
The reliability of the data in Table 2 was
determined in 10 women with a singleton intrauter-
ine pregnancy resulting from in-vitro fertilization.
The mean gestational sac diameter was determined
through transvaginal ultrasonography, and the gesta-
tional age expected from Table 2 was compared with
the actual age. The variability observed between
expected and actual gestational age was 1 day (mean
0.2 [SD 0.6] days) (Table 3).
(in days) =
Estimation of gestational age on the basis of
knowledge of the last menstrual period is well known
to be error-prone. Our results further support this
e nte,!v J
'd 40.) 6
42 5 43.
68 8-- 60 4
44, ... ,
esationaI age iva
CAN MED ASSOC J 1991; 144 (4)
Mean sac diameter, mm
observation, since a greater degree of variability was
observed when menstrual data were used than when
hCG measurements were used. Also, the use of the
normal hCG curve to correct for uncertainties in the
date of ovulation has been shown to predict gesta-
tional age accurately."'12
Our findings confirm that an intrauterine gesta-
tional sac can be detected very early with the use of
transvaginal ultrasonography and that the hCG
threshold level is much lower than previously report-
ed with the use of transabdominal ultrasonography.
Because of the small number of cases in which no
sac was visualized
threshold level could not be determined reliably
from our data. Nevertheless, a gestational sac was
not observed when the hCG level was less than 1100
a practical hCG
Fig. 3: Mean diameter of gestational sac and corresponding
estimates of gestational age. Solid line represents mean
gestational age, dotted lines represent upper and lower
limits of 95% confidence interval, and broken lines repre-
sent upper and lower limits of95% PI.
IU/L. This was further reinforced in our subsequent
study in which we correlated hCG levels with gesta-
tional sac diameter.'3 By extrapolating the curve and
calculating the upper 95% PI at a mean sac diameter
of 0 mm we found that the hCG level obtained was
1079 IU/L. Similar hCG levels have been reported
by others.'4"'5 One group of investigators identified a
gestational sac at much lower hCG levels;'6 however,
since they did not state which hCG standard was
used it is tempting to speculate that it was the 2nd
The fact that during early pregnancy the rate of
growth of the gestational sac is linear enables the
true gestational age to be calculated. Using the
regression equation we tabulated the expected gesta-
tional ages so that the mean sac diameter could be
converted to the corresponding gestational age. This
table was shown to be very reliable and precise in the
assessment of pregnancies conceived through in-
vitro fertilization. Therefore, it can be used clinically
to determine gestational age. One gold standard used
for ultrasonic assessment of gestational age requires
precise measurement of the crown-rump length.
This measurement is usually not possible until later
in the first trimester, when the fetus can be clearly
visualized. However, with the use of transvaginal
ultrasonography the gestational age can now be
accurately determined through the measurement of
the sac diameter. Furthermore, one can monitor a
pregnancy by comparing the size of the gestational
sac in two ultrasound examinations performed sever-
al days apart. This method may provide useful
prognostic information to women with a history of
recurrent abortion who are carefully monitored by
ultrasonography in early pregnancy and to women
who are spotting in early pregnancy, especially if
appropriate growth in sac size is observed.
Early identification of intrauterine pregnancy
could also improve clinical management of ectopic
CAN MED ASSOC J 1991; 144 (4)
r - 0.95
Mean sac diameter, mm
Table 3: Actual and expected gestational ages in 10 pregnancies
conceived through in-vitro fertilization
*Actual gestational age was calculated by retrospectively assigning the day of oocyte
retrieval as day 14 of gestation. Expected gestational age was obtained from Table 2
after the sac diameter was determined through transvaginal ultrasound scanning.