- Can the anterior-posterior thigh diameter be used as an indicator for fetal age using two-dimensional sonography?
SAAD RAMZI ISMAIL;
Please read my full paper , published with the JSDMS -USA. This research won the 3rd prize Canadian excellence in Sonography award -CHASMS,2005.FOR more information regarding this research please search google under my name Saad ramzi Ismail and then put APTD .My research was also published in the RADIOGRAPHER JOURNAL -The South African Radiographer | ISSN 0258 0241 . 2005. This study was approved by the Ethics Committee of Charles Sturt University, Australia as my MSc thesis project in Medical Ultrasound.
February 2008 Volume 14, Issue 1, Pages 45–51
Abstract:
This study evaluates the usefulness and direct correlation of a new method of predicting fetal age by the measurement of the anterior posterior high diameter (APTD) in normal 18 to 28 week pregnancies using two-dimensional sonography. Little published research exists in the area of fetal thigh biometry, specifically in the use of the APTD. The only study the author found was that of fetal thigh circumference. Continuing review of existing practices needs to be coupled with evaluation of alternate or additional methodology.
Material and methods:
This was a quantitative prospective study of 55 patients in a hospital in Alberta, Canada. APTDs were sonographically
measured. The normal range for each week of pregnancy was determined for reliability.
Results:
Significant correlation was found between the APTD and fetal age from simple line regression analysis, with 99.9% confidence intervals at each week from 18 to 28 weeks gestation. There was a correlation of 1 mm APTD per one week of fetal age. In addition R >0.93, P< than 0.001. The residual scatter plots confirmed the APTD validity.
Conclusion:
APTD is a reliable and valid method for assessing fetal age in a normal pregnancy and may be particularly useful when other parameters are unable to accurately predict fetal age. An accurate linear measurement of multiple fetal parameters allows a more complete profile of fetal growth and estimated date of delivery. APTD may also be useful in identifying fetal growth problems. All of the values of fetal age lie directly on the best-fit regression line. Since the coefficient of determination (Rsq) is very high, this model is very effective.
Can the anterior-posterior thigh diameter be used as an indicator for fetal age using two-dimensional sonography?
This study evaluates the usefulness and direct correlation of a new method of predicting fetal age by the measurement of the anterior posterior, thigh diameter (APTD) in normal 18 to 28 week pregnancies using two-dimensional sonography. Little published research exists in the area of fetal thigh biometry, specifically in the use of the APTD. The only study the author found was that of fetal thigh circumference. Continuing review of existing practices needs to be coupled with evaluation of alternate or additional methodology.
Material and methods: This was a quantitative prospective study of 55 patients in a hospital in Alberta, Canada. APTDs were sonographically measured. The normal range for each week of pregnancy was determined for reliability.
Results: Significant correlation was found between the APTD and fetal age from simple line regression analysis, with 99.9% confidence intervals at each week from 18 to 28 weeks gestation. There was a correlation of 1 mm APTD per one week of fetal age. In addition R >0.93, P< than 0.001. The residual scatter plots confirmed the APTD validity.
Conclusion: APTD is a reliable and valid method for assessing fetal age in a normal pregnancy and may be particularly useful when other parameters are unable to accurately predict fetal age. An accurate linear measurement of multiple fetal parameters allows a more complete profile of fetal growth and estimated date of delivery. APTD may also be useful in identifying fetal growth problems. All of the values of fetal age lie directly on the best-fit regression line. Since the coefficient of determination (Rsq) is very high, this model is very effective.
Keywords: APTD, parameters, weight estimation, biometry.
APRIL 2007 volume 45 number 1 THE SOUTH AFRICAN RADIOGRAPHER
The participants were chosen by randomized selection of normal
pregnancies. All participants had an early (first trimester) sonogram at 12
week gestation to confirm the accuracy of the gestational age.
The author performed the study and compiled comparable data and
tables with the Hadlock et al tables for FL [31, 32]. The growth of the
APTD, outer to outer skin surface, was sonographically measured at the
middle point of the fetal femur in the sagital section and compared with
the fetal age from 18 to 28 weeks gestation. The second trimester period
was chosen because soft tissue accretion of the fetal thigh begins to
accelerate towards the end of this period.
The inclusion criteria for this study were: singleton uncomplicated
pregnancies with a normal fetus, and an informed consent form, read and
signed by the participants and approved by the hospital and Charles Sturt
University Ethics Committee.
The participants’ ages ranged between 18 and 35 years, with a mean
age of 26.5. The study population was of different ethnic groups in Alberta,
Canada, for example, Germans, natives Indians, Mennonites, Irish,
Hispanics, Ukrainians and east Indians.
Radiologists reported major congenital malformations, chromosomal
abnormalities, and maternal complications. The author did not release any
pathology information to the participants as they were informed to obtain
their reports from their physicians.
Routine transabdominal sonography was performed, including FL, BPD,
AC, and head circumference (HC). In addition, the author measured the
fetal APTD, from the middle point of the fetal femur in the sagittal section
of the fetal thigh using the femur length as a landmark. The APTD
measurements were analyzed and compared with fetal age using Hadlock
et al tables for femur length [31, 32].
Equipment used in this study was ATL 5000 and Philips Alegra 4500
(Bothell, WA). With 5 to 3 MHz transducers the fetal age was determined
by using measurements of the FL [31, 32].
A comparison was made between the APTD and the fetal age. The
diameter of the fetal thigh was measured in the same portion of fetal thigh
every time by measuring the mid-point of the femur. Eleven groups were
studied. Each group comprised five participants who were all in the same
pregnancy period, namely from 18 to 28 weeks.
Protocol used in this study
Starting with transducer at the fetal abdominal circumference.
1. Transducer was moved inferiorly to transect the fetal bladder.
2. Transducer was rotated 30 degrees to view the fetal femur.
3. Transducer was rotated until a sagittal view of the fetal thigh was
obtained (Figure 1).
4. Distal femoral epiphyses which are usually present after 32 weeks
gestation were excluded.
5. The fetal knee was identified.
6. In cases when a double line was seen in the fetal thigh the inner
line was measured or the scan was repeated until a smooth
(sagittal) line of the fetal thigh was obtained (Figure 2). Note that
this double line can be corrected by obtaining a perfect sagittal
view of the fetal thigh. Otherwise the curve of the thigh adds extra
false line to the real outer skin surface of the fetal thigh in the
lateral or medial section. The thigh is convex in the anterior part
and concave in the posterior part so geometrically we are dealing
with a cylinder and not a flat surface.
7. Real-time sonographic equipment was used with 3.0, 3.5, and 5.0
MHz transducers frequencies to obtain the images. Note that
posterior shadowing from the femur bone is limited and will not
affect the over all measurements.
8. Freeze-frame and electronic calipers were used as they are more
sensitive tools to provide accurate measurements of the fetal
thigh.
9. Zoom capability was used to outline the fetal thigh, namely the
outer skin surface which allowed the author to see the skin surface
better therefore the chances of errors were reduced.
10. Hadlock et al table for FL [31, 32] was used to compare with
APTD
Measurements
The FL of the fetus was scanned in each of the pregnant participants as a
sagittal view (Figures 1 and 2).
Figure 1. Label A is showing the wrong way to measure fetal thigh (coronal)
and Label B is showing the correct way to measure the anterior-posterior
thigh diameter (APTD) in sagittal plane (profile).
Figure 3. The sagittal section of the fetal thigh is showing the measurement
of the femur length. The arrow is showing the fetal knee.
Magnification can be a helpful tool.
Figure 2. The white arrow is showing the double line of the fetal thigh. The
correct measurement of the anterior-posterior thigh diameter would be the
second line marked by the number (1) arrow in the real anterior wall of the
fetal thigh; as this is the true skin line. The second line marked by number (2)
arrow is part of the thigh tissue as the sound waves travels through the
convex area can be corrected by scanning in a good sagittal plane.
Figure 4. Sagittal plane of the fetal thigh is showing the femur length with
one of the calipers in the mid point of the femur length.
THE SOUTH AFRICAN RADIOGRAPHER volume 45 number 1 APRIL 2007
16
1. The femur length was measured using callipers, namely first
caliper placed in exact middle point of the fetal femur; for example,
if the femur length was 2.4 cm then the first calliper was moved
until the measurement read 1.2 cm (Figures 3 and 4).
2. The first calliper was carefully moved to the outer surface of the
fetal anterior thigh (Figure 5); the skin surface was measured and
not the extra double line created by the sound waves that travel
through the convex part of the thigh in para-sagittal planes. Note
that scanning the fetal thigh in the sagittal plane can make
correction and smooth the skin surface of the fetal thigh. The
second calliper was moved to the outer surface of the posterior
thigh, and entered (Figure 6).
Calculations
Each one millimetre of the APTD, or the posterior-anterior thigh diameter
(PATD) measurements was taken to be equal to one-week. For example,
1.90 cm will be equal to 19 weeks gestation, and 2.80 cm will be equal to
28 weeks gestation. Multiply 1.428 with any fraction of a millimetre. This
number 1.428 was obtained from 10 mm divided by 7 days, for example,
APTD of 2.68 cm (26.8 mm) calculates to 26 weeks plus 0.8 x 1.428 =
0.1424 day. This is added to the 26 weeks equalling 27.0 weeks and 1.4
day. The APTD was found to be relatively constant, one mm equal to one
week.
Serial measurements should however be obtained. The measurements
should be repeated with zooming capability and electronic callipers; the
serial measurements range should be less than 1 mm. If these
measurements do not match the fetal age obtained by using Hadlock et al
tables for FL [31, 32] a follow-up scan should be recommended.
Results
Measurements of fetal femur lengths of the 55 pregnant participants who
met the criteria were correlated with the APTD and used to construct
tables and graphs. There was significant correlation between the APTD and
fetal age. Using a simple linear regression for this study, more than 99.9
% confidence intervals were found at each week of the eleven groups from
18 to 28 weeks gestation (R > 0.93), and (p less than 0.001). The APTD
was positively correlated with fetal age (Table 1 and Graphs 1, 2, 3 and 4).
Eleven gestational periods from 18 to 28 weeks were analyzed, each
period included five different measurements of the femur lengths
compared to the fetal age and to the ATPD with mean +/-2SD. Femur
length measured from 2.70 cm to 5.50 cm over all gestational periods, the
mean being 4.3. Fetal weight ranged between 310 grams and 1400
grams, the mean being 629 grams. The APTD ranged between 1.80 to
2.87 cm, with the mean at 2.36 cm. Linear growth was obtained in each
gestational period from 18 to 28 weeks, and compared with the Hadlock et
al tables [31, 32]. In addition a linear growth of fetal weight was observed
in the graphs (see Graph 1). The ATPD when converted to millimetres and
compared with the fetal age, was found to be a consistent and valid
measurement by using the scatter plots (Graphs 2 and 3). The standard
error of estimates using the APTD was significantly lower at .08664 than
that using femur length at .2436. The variability estimates from Hadlock et
al table [31] for femur length versus fetal age from 18 to 30 weeks have
indicated ±1.8 weeks to 2.4 weeks. The APTD table in this study shows
±3 days variability (see Table 1). Adjusted R square variance was >.99 for
both models.
Statistical analysis
Regression: APTD (cm) and fetal age (weeks)
The standard error of estimation is very low at .08664. This indicates a
strong good fit of this model. The spread of values for the dependent
variable, fetal age, around the mean value of the independent variable is
very narrow. About 70% of the values of fetal age will lie ± .08664 from
the mean of APTD using a nova method.
Discussion
The simplicity of the application found by this study is really its greatest
advantage. The idea is new as the only study done previously was the fetal
Figure 5. The first caliper is moved to the real outer skin of the anterior wall
of the fetal thigh.
Figure 6. The second caliper is moved to the posterior wall of the fetal thigh.
Enter and log the measurement of the anterior posterior
thigh diameter (APTD).
Graph 1: Regression Line for APTD
All of the values of fetal age lie directly on the “Best Fit” Regression Line.
Graph 2: Regression Line for Femur Length and Gestational age.67
Some of the values of fetal age in Dr Hadlock’s model lie
slightly above or slightly below the “Best Fit” Regression Line.
R Square was .994 and SEE was .24362.
thigh circumference and not the APTD. Accuracy of fetal age, weight, and
estimated delivery date should be improved if multiple predictors are used,
especially when it is difficult to obtain fetal head biometry; for example,
when the head is too low in the pelvis, hydrocephalus, anencephaly, and
fetal renal disease.
New methods for estimating fetal body weight and fetal age without
head measurement are therefore required. Reliable new methods of fetal
biometry could be very beneficial in reducing overall fetal biometry errors
and increasing the reliability of fetal biometry. Results of this study show
that the ATPD predicts second trimester growth with high validity and
reliability.
The very simple correlation in this study of 1 mm APTD per week of
fetal age is new and useful information. Measuring thigh parameter can be
a convenient method for determining fetal growth in the second trimester.
The APTD may have a role in quality control of second trimester sonogram
examination and may help in the diagnosis of fetal growth abnormalities.
The APTD may be used as an indicator of fetal biometric disturbance
enabling the physician to better manage the pregnancy. Diabetes mellitus
is one cause of intrauterine growth restriction (IUGR), and may affect the
femur length [10,23,27]. Diabetes mellitus may also affect the fetal body
mass and consequently the abdominal circumference and fetal thigh [28]
hence the APTD can be used not only as indictor for fetal age but also to
detect IUGR. Renal pathology, such as hydronephrosis or congenital renal
malformation, can affect the fetal abdominal circumference, making this
measurement unreliable as an indicator of fetal age. Using combined
parameters may be superior to the use of each measurement alone as a
Table I. Correlation between anterior-posterior thigh diameter (APTD-CM) and fetal age (GA-WK) 50th percentile values for fetal femur length
are shown below, (n=55).
Femur Length
(cm) From
Hadlock Table67, 68
Fetal age (wk)
using Hadlock
Graph 3: the residual (error), scatter plot and validity of the APTD
Normally distributed residuals scatter plot
Graph 4: Residual (error) scatter plot – femur length from Dr Hadlock’s Table
67. Pattern of residuals show curvilinear relationship with regression line
marker of trisomy 21 [30]. In addition, it can be difficult in practice to
obtain a good fetal thigh circumference, or fetal hands, feet and ears to
obtain fetal biometry. This study shows that the fetal APTD provides a more
accurate linear measurement of the fetus, thus generating a more
complete profile of the fetus.
Significant correlations of APTD with fetal age indicate that this is a
reliable method and is particularly useful when other fetal parameters may
not accurately predict fetal age or if they are difficult to obtain. If the age
predicted from the APTD does not match the age using the femur length,
other factors, such as intrauterine growth restriction or maternal and fetal
nutrition deficits, should be considered.
The soft tissue accretion of the fetal thigh also depends on the
generalized nutritional status of the fetus but such increase in the soft
tissue is usually more marked after the 30th week of gestation. The APTD
measurements obtained from the 11 groups correlated well with the fetal
age and repeated five times for each gestational group between 18 and 28
weeks.
Tables for femur length versus gestational age from 18 to 30 weeks
were ± 1.8 to ± 2.4 weeks while the variability estimates in the APTD
table was ± 3days. Both models predict the fetal age very well, but
compared to FL using APTD produces a model with better goodness of fit
based on differences in the standard error of estimates (SEE) between the
two of them, and on interpreting the best fit regression lines for both
models. The spread of values for the dependent variable is narrower
around the mean of the independent variable in the APTD model and wider
in the FL model.
The SEE of .2436 obtained for FL versus gestational age is higher than
that obtained in the analysis with APTD. This indicates a weaker goodness
of fit of this model. The spread of values for the dependent variable around
the mean value of the independent variable is wider; 68% of the values of
fetal age will lie ± .2436 from the mean of APTD. Model statistics (F, t, and
standardized Beta) are significant for both models. Beta (APTD) = 10.0
(SEE = . 037), Beta (FL) = 3.79 (SE = . 039). T =273.07 for GA x APTD
Model = 96.87 for GA x FL Model
Conclusion
APTD was found to be a valid and reliable index for estimating fetal age.
Further research to study the relationship between APTD versus fetal
weight and IUGR is needed. More research is also needed to study the
APTD measurements from 12 to 40 weeks gestational age and in a larger
population in order to be more statistically significant.
Declaration
No financial support was granted to this research and no commercial
affiliation was involved.
Acknowledgements
The author wishes to express his deepest appreciation to his project
supervisors Dr Karen Hofmann and Karen Pollard for their guidance and
advice. In addition thank you to DR Philip Hughes, S Desilva, A Zammit, Gary
Kachure, Dr K Game, Dr V Botha, and Dr S Benade for their assistance.
Grateful thank you to Ms Jean Spitz, Valletta Lawrence, and Siti Arabiah.
This research is dedicated to the memories of my parents and brothers.
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February 2008Volume 14, Issue 1, Pages 45–51
Can the anterior–posterior thigh diameter be used as an indicator for fetal age using two-dimensional sonography?☆
Saad Ramzi Ismail, PhD. Calgary- Alberta
Abstract
This study evaluated the usefulness and direct correlation of a simple new method of predicting fetal age by measurement of the anterior–posterior thigh diameter (APTD) in a normal 18 to 28 week pregnancies using two-dimensional sonography. Little published research exists in the area of fetal thigh biometry, specifically in the use of the anterior–posterior fetal thigh diameter (APTD). The only study I found was that of fetal thigh circumference. Continuing review of existing practices needs to be coupled with evaluation of alternate or additional methodology.
Materials and methods
This was a quantitative prospective study of 55 patients in High Level General Hospital, Alberta, Canada. Anterior–posterior thigh diameters (APTD) were sonographically measured. The normal range for each week of pregnancy was determined five times for reliability.
Results
Significant correlation was found between (APTD) and fetal age from simple line regression analysis, with 99.993% confidence intervals at each week from 18 to 28 weeks gestation. There was a correlation of 1 mm APTD per 1 week of fetal age. In addition R > 0.93, P < 0.001. The residual scatter plots confirmed the APTD validity.
Conclusion
APTD is a reliable and valid method for assessing fetal age in a normal pregnancy and may be particularly useful when other parameters are unable to accurately predict fetal age. An accurate linear measurement of multiple fetal parameters allows a more complete profile of fetal growth and estimated date of delivery (EDD). APTD may also be useful in identifying fetal growth problems. All of the values of fetal age lie directly on the “best-fit” regression line. Since the coefficient of determination (Rsq) is very high, this model is very effective.