Biometria 11 14

Ultrasound Obstet Gynecol 2002; 20: 564–574

Fetal transabdominal biometry at 11–14 weeks of gestation
Blackwell Science, Ltd

C.S. VON KAISENBERG*, E. FRITZER*, H. KÜHLING* and W. JONAT*
*Department of Obstetrics and Gynecology, University of Kiel, Kiel, Germany

K E Y W O R D S: Biometry, First trimester, Growth charts, Nuchal translucency, Skeletal dysplasia

A BSTRACT INTRODUCTION
Objective To establish comprehensive transabdominal ultra- Previous studies during the first trimester have predomin-
sonographic reference ranges for viable normal singleton antly used transvaginal ultrasound to assess parameters
human fetuses at 11–14 weeks’ gestation. such as the gestational sac, amniotic sac and yolk sac, the
embryonic or fetal crown−rump length (CRL), the biparietal
Methods Single transabdominal ultrasound measurements parameter and the femur length. Their main aim was to
were taken once per pregnancy at a gestational age of determine the gestation from ultrasound examination and
between 11+0 and 14+0 weeks (crown−rump length, 45– to predict the estimated date of delivery or to search for
84 mm), in viable singleton fetuses with nuchal translucency ominous signs of pregnancy failure1–9. Further studies
≤ 3 mm and without detectable structural anomalies, using established first-trimester transvaginal growth charts for
four standard planes: (i) biparietal diameter (BPD) and the biparietal diameter (BPD), head circumference (HC),
fronto-occipital diameter (FOD) resulting in head circumfer- transverse cerebellar diameter (TCD), abdominal diameters
ence (HC), anterior horn (Va), posterior horn (Vp), and hemi- and abdominal circumference, femur and humerus length,
sphere (HEM); (ii) transcerebellar diameter (TCD) and and foot length8.
cisterna magna (CM); (iii) abdominal anteroposterior (AAP) The objective of this study was to create comprehensive
and abdominal transverse diameter (ATD) resulting in growth charts using transabdominal ultrasound at 11–14
abdominal circumference (AC); and (iv) femur length (FL). weeks, the gestational age at which nuchal translucency (NT)
The respective ratios Va/HEM, Vp/HEM, HC/AC, BPD/FL, is measured. Such charts may facilitate the interpretation of
BPD/FOD, FL/CRL, FL/BPD and FL/AC and the estimated first-trimester biometry regarding early onset symmetrical
weight were derived. Reference ranges were constructed or asymmetrical growth restriction, the interpretation of
and the mean and 5th and 95th centiles were plotted against abnormal measurements associated with aneuploidies, and
gestation. the detection of severe forms of skeletal dysplasias.
Results There was a general increase in biometric parame-
ters with gestation. The ratios for the ventricles vs. hemi- M ET H O D S
sphere and BPD/FL ratio decreased while the BPD/FOD and
HC/AC ratios remained constant. Analysis of the reference Only viable singleton pregnancies were included in the study.
range for BPD/FL was performed in both 167 and 664 Each fetus was measured once during the period 11–
fetuses and the results showed almost the identical type of 14 weeks (CRL, 45–84 mm). In all cases, there was an unre-
equation, indicating a high degree of accuracy for the growth markable maternal history including a regular menstrual
charts. period and absence of oral contraception or pregnancy dur-
ing the previous 3 months. No correction of dates using the
Conclusions We have established comprehensive reference CRL was performed. In all cases, a CRL was taken and NT
ranges for first-trimester fetal biometry by transabdom- was 0.7–3 mm and there were no obvious structural fetal
inal sonography. These charts may have a role in the anomalies. Fetuses which subsequently miscarried and those
diagnosis of early onset symmetrical or asymmetrical with chromosomal abnormalities were excluded from the
growth restriction and in the interpretation of measure- calculation of normal reference ranges. All measurements
ments in chromosomally abnormal fetuses, and they were performed by one experienced sonographer using
may help in the detection of skeletal dysplasias or acrania/ transabdominal ultrasound (ATL SonoCT and tissue har-
anencephaly. monic imaging software, ATL (Philips), Solingen, Germany).

Correspondence: Dr C.S. von Kaisenberg, Department of Obstetrics and Gynecology, University of Kiel, Michaelisstr 16, 24105 Kiel, Germany
(e-mail: vkaisenberg@email.uni-kiel.de)
Accepted 28-08-02

564 ORIGINAL PAPER

First-trimester biometry von Kaisenberg et al.

This sonographer was a holder of The Fetal Medicine anterior and posterior cerebral ventricle diameter (Va and
Foundation’s Certificate of Competence for first-trimester Vp), and hemisphere (HEM) were obtained from a transverse
scanning and the unit had been a first-trimester training center axial plane of the fetal head showing a central midline echo
for several years. broken in the anterior third by the cavum septi pellucidi, if
No reproducibility studies were carried out, but previous already present, and demonstrating the anterior and pos-
studies investigating variability for NT measurements found terior horns of the lateral ventricles. BPD and FOD were
that in 95% of cases the intraobserver, interobserver and cal- measured from the outer border of the skull and HC was
iper placement repeatability of measuring fetal NT were less calculated (3.14 × (BPD + FOD)/2). Va was the distance
than 0.54 mm, 0.62 mm and 0.58 mm, respectively10. The between the lateral wall of the anterior horn to the midline
measurements under investigation in this study were larger and Vp was the distance between the medial and lateral walls
than normal NT measurements and therefore it could be rea- of the posterior horn. The hemisphere was measured from
sonably assumed that, with the same standard of scanning as the midline to the inner border of the skull. TCD and cisterna
for NT, the potential relative variability would be much magna diameter (CM) were measured in the suboccipito-
lower in this study than for the NT study10. bregmatic plane of the head. The femur length (FL) was meas-
Four planes were used as previously described for the ured from the greater trochanter to the lateral condyle. For
second trimester11 and examples are shown in Figures 1–4. abdominal circumference (AC), a transverse section of the
Measurements of BPD, fronto-occipital diameter (FOD), fetal abdomen was obtained at the level of the stomach and

Figure 1 Axial standard view of the fetal skull and brain showing the falx cerebri, cavum septi pellucidi and lateral ventricles with the choroid plexus
at 20 weeks (left) and at 13+3 weeks (right) and the respective measurements biparietal diameter, fronto-occipital diameter, anterior horn, posterior
horn and hemisphere.

Figure 2 Axial standard view of the skull, showing the cerebellum and cisterna magna at 20 weeks (left) and at 13+3 weeks (right) and the respective
measurements transcerebellar diameter and cisterna magna.

Ultrasound in Obstetrics and Gynecology 565


Figure 3 Transverse standard view through the fetal abdomen, showing the spine, ribs, stomach, and bifurcation of the portal vein at 20 weeks (left)
and at 13+3 weeks (right) and the respective measurements abdominal anteroposterior diameter and abdominal transverse diameter.

Figure 4 Longitudinal standard view of the fetal femur at 20 weeks (left) and at 13+3 weeks (right) and the measurement of femur length.

the bifurcation of the main portal vein into its right and left a Gaussian distribution with a mean and standard deviation
branches. The anteroposterior (AAP) and transverse (ATD) and that, in general, both vary smoothly with gestational age.
diameters were measured and AC was calculated (3.14 × The estimation of functions for mean and standard deviation
(AAP + ATD)/2). The following ratios and the estimated fetal is based on regression analysis. If the deviation increases
weight12 (BPD,AC) were calculated: HC/AC, BPD/FL, BPD/ strongly with gestational age, it is easier to model the loga-
FOD, Va/HEM, Vp/HEM11. Subsequently, FL/CRL, FL/BPD rithm of the measurements than the original values. In this
and FL/AC were derived. Measurements were stored in the study this had to be done seven of 21 times. After the invest-
Fetal Database (Viewpoint, General Electrics, Wesling, igation of the deviation the function for the mean is calcu-
Germany). Statistical analysis was carried out and reference lated by using a least-squares regression analysis. First a cubic
ranges were calculated using a mathematical model described polynomial is fitted. If the cubic coefficient is not significantly
by Royston and Wright13. We obtained the mean and 5th and different from zero, then a quadratic polynomial is fitted and
95th centiles for 11+0, 12+0, 13+0, and 14+0 weeks and the same assessment is made of the quadratic coefficient. This
measurements were plotted against gestation. process is repeated until no further removal of terms is pos-
sible. If it is necessary to fit polynomials of degrees higher
than cubic, fractional polynomials should be used; however,
Details of statistical methods
in this study this was not necessary. When the measurement
The calculation of reference ranges for the biometry meas- has approximately a Gaussian distribution, the fitted values
urements of the 11–14-week scan followed closely the pro- following regression of scaled absolute residuals on age are
cedure described by Royston and Wright13. This method an estimation of the standard deviation curve. If there is
assumes that, at each gestational age, the measurements have no trend with gestational age, the standard deviation is

566 Ultrasound in Obstetrics and Gynecology


estimated as the standard deviation of the unscaled residuals. identical type of equation, indicating a high degree of accur-
If there is a trend, then polynomial regression analysis is acy for the growth charts. Measurements for TCD (n = 120) and
needed in the same way as for the mean. The assumption of a CM (n = 117) could not be taken in all cases from 11+0
Gaussian distribution is tested by using Z-scores. A normal weeks, but at 14 weeks the average score for the cerebellum
probability plot of the Z-scores gives an impression of the was 3.2 (scores: 1, not seen; 2, uncertain seen; 3, accept-
degree to which the values follow a Gaussian distribution. able seen; 4, well seen; 5, very well seen), which is compatible
This can be verified formally by the Shapiro−Francia W′ test14 with the observation that the cerebellum can be measured
and by the Shapiro−Wilk test15,16 and all P-values using both transabdominally in nearly all cases at 14 weeks.
tests were > 0.05. A plot of the Z-scores against gestational All fetal biometric parameters showed an increase with
age should be randomly scattered about zero. If there appears gestation. The ratios for the ventricles and the BPD/FL ratio
a trend or there is a deviation from a Gaussian distribution, decreased while the BPD/ FOD and HC/AC ratios remained
then the whole computation must be done again after a suit- constant with increasing gestation. The distribution of normal
able transformation of the measurements. However, in this ranges and numbers per week are provided in Tables 1–22.
study this was not the case. Once a satisfactory model has been Equations for calculation of the mean and centiles for each
determined, the centile curves for the reference interval are parameter are given in Table 23.
calculated by substituting the expressions for the mean and
standard deviation into the following equation: centile = mean
DISCUSSION
+ K × standard deviation, where K is the corresponding cen-
tile of the standard Gaussian distribution. If the estimation All fetal biometric parameters showed an increase with ges-
of the curves is done on a log scale, this must be considered. tation while the ratios for the ventricles and the BPD/FL ratio
decreased and the BPD/ FOD and HC/ AC ratios remained
constant with increasing gestation. Previous studies at 14–
RE SUL TS
40 weeks’ gestation have established likelihood ratios for
Measurements for FOD (n = 167), Va (n = 162), Vp (n = 162), fetal chromosomal defects using specific alterations of fetal
HEM (n = 162) and AAP and ATD (n = 164) were made. biometry such as brachycephaly (BPD/ FOD > 95th centile),
Measurements for BPD (n = 675) and FL (n = 664) were taken ventriculomegaly (Va/ HEM or Vp/ HEM > 95th centile),
more frequently as part of the routine for the first-trimester microcephaly (HC < 5th centile), enlarged cisterna magna
scan, which also included CRL (n = 660) and NT (n = 660). (CM > 95th centile), short femur (FL < 5th centile or BPD/
An analysis of the reference range for BPD/FL was performed FL > 95th centile), and small-for-gestational age (AC < 5th
in both 167 and 664 fetuses and the results showed an almost centile)17. The CRL of trisomy 18 fetuses is known to be

Table 1 Distribution of measurements for the crown−rump length (mm)
against gestation (weeks), 90% confidence interval (n = 660)

Weeks 5th centile Mean 95th centile

11+0 40.5 46.8 53.2
12+0 49.6 58.6 67.6
13+0 60.9 70.4 79.8
14+0 74.6 82.1 89.6

Table 2 Distribution of measurements for the biparietal diameter (mm)


11+0 14.1 17.3 20.5
12+0 17.7 20.9 24.1
13+0 21.4 24.5 27.7
14+0 25.0 28.2 31.3



Table 3 Distribution of measurements for the fronto-occipital diameter
(mm) against gestation (weeks), 90% confidence interval (n = 167)


11+0 15.9 19.8 23.7
12+0 20.5 24.4 28.3
13+0 25.1 29.0 32.9
14+0 29.7 33.6 37.5

Table 4 Distribution of measurements for the head circumference (mm)


11+0 47.1 57.2 67.3
12+0 60.5 70.6 80.7
13+0 73.9 84.0 94.1
14+0 87.3 97.4 107.5

Table 5 Distribution of measurements for the cisterna magna (mm)


11+0 0.9 1.4 2.0
12+0 1.1 1.6 2.4
13+0 1.3 2.0 2.9
14+0 1.6 2.3 3.4

Table 6 Distribution of measurements for the transverse cerebellar dia-
meter (mm) against gestation (weeks), 90% confidence interval
(n = 120)


11+0 5.2 6.7 8.5
12+0 7.1 9.1 11.6
13+0 8.6 11.0 14.0
14+0 9.1 11.7 15.0



Table 7 Distribution of measurements for the anterior cerebral ven-
tricle (mm) against gestation (weeks), 90% confidence interval (n = 162)


11+0 2.2 3.3 4.4
12+0 3.0 4.1 5.2
13+0 3.8 4.9 6.0
14+0 4.6 5.7 6.7

Table 8 Distribution of measurements for the posterior cerebral ven-
tricle (mm) against gestation (weeks), 90% confidence interval (n = 162)


11+0 2.2 3.1 4.0
12+0 2.9 4.0 5.1
13+0 3.7 5.0 6.3
14+0 4.4 5.9 7.4

Table 9 Distribution of measurements for the hemisphere diameter


11+0 4.8 6.4 8.0
12+0 6.4 8.0 9.6
13+0 8.0 9.6 11.2
14+0 9.6 11.2 12.8

Table 10 Distribution of measurements for the abdominal transverse
diameter (mm) against gestation (weeks), 90% confidence interval
(n = 164)


11+0 12.8 15.0 17.6
12+0 15.4 18.1 21.3
13+0 18.6 21.8 25.7
14+0 22.4 26.3 30.9



Table 11 Distribution of measurements for the abdominal
anteroposterior diameter (mm) against gestation (weeks), 90%
confidence interval (n = 164)


11+0 12.2 14.3 16.4
12+0 15.2 18.1 21.1
13+0 18.1 21.9 25.7
14+0 21.1 25.7 30.4

Table 12 Distribution of measurements for the abdominal circumference


11+0 35.7 45.4 55.1
12+0 47.5 57.2 66.9
13+0 59.4 69.1 78.8
14+0 71.2 80.9 90.6

Table 13 Distribution of measurements for the femur length (mm)


11+0 3.2 4.8 7.0
12+0 4.7 6.6 9.2
13+0 6.8 9.1 12.2
14+0 9.9 12.6 16.1

Table 14 Distribution of the ratio of anterior cerebral ventricle dia-
meter (Va) to hemisphere (HEM) against gestation (weeks), 90%


11+0 0.349 0.513 0.678
12+0 0.379 0.513 0.647
13+0 0.410 0.513 0.616
14+0 0.441 0.513 0.585



Table 15 Distribution of the ratio of posterior cerebral ventricle dia-
meter (Vp) to hemisphere (HEM) against gestation (weeks), 90%


11+0 0.356 0.504 0.714
12+0 0.377 0.504 0.675
13+0 0.398 0.504 0.639
14+0 0.421 0.504 0.604

Table 16 Distribution of the ratio of head circumference (HC) to
abdominal circumference (AC) against gestation (weeks), 90%


11+0 1.085 1.231 1.376
12+0 1.085 1.231 1.376
13+0 1.085 1.231 1.376
14+0 1.085 1.231 1.376

Table 17 Distribution of the ratio of biparietal diameter (BPD) to femur
length (FL) against gestation (weeks), 90% confidence interval (n = 664)


11+0 2.626 3.709 5.239
12+0 2.347 3.152 4.232
13+0 2.097 2.678 3.420
14+0 1.873 2.275 2.764

Table 18 Distribution of the ratio of biparietal diameter (BPD) to
fronto-occipital diameter (FOD) against gestation (weeks), 90%


11+0 0.766 0.846 0.926
12+0 0.766 0.846 0.926
13+0 0.766 0.846 0.926
14+0 0.766 0.846 0.926



Table 19 Distribution of measurements for the ratio of femur length
(FL) to crown−rump length (CRL) against gestation (weeks), 90%


11+0 0.069 0.104 0.139
12+0 0.081 0.115 0.149
13+0 0.098 0.132 0.166
14+0 0.120 0.155 0.189

(FL) to biparietal diameter (BPD) against gestation (weeks), 90%


11+0 0.188 0.283 0.378
12+0 0.228 0.323 0.418
13+0 0.285 0.380 0.475
14+0 0.358 0.453 0.548

(FL) to abdominal circumference (AC) against gestation (weeks), 90%


11+0 0.062 0.093 0.123
12+0 0.083 0.114 0.144
13+0 0.104 0.134 0.165
14+0 0.125 0.155 0.186

Table 22 Distribution of the estimated fetal weight (BPD,AC)12 against
gestation (weeks), 90% confidence interval (n = 158)


11+0 52 61 71
12+0 65 75 88
13+0 80 93 108
14+0 99 115 134



Table 23 Equations for calculation of mean and centiles Table 23 Continued

Crown–rump length (CRL) BPD/FOD
Mean −82.4827 + 11.7565·wks Mean 0.8461
5th centile 30.8275 − 2.7528·wks + 0.0300·wks3 5th centile 0.7661
95th centile −195.7929 + 26.2658·wks − 0.0300·wks3 95th centile 0.9260
Biparietal diameter (BPD) FL/CRL
Mean −22.5100 + 3.6190·wks Mean 0.3696 − 0.0565·wks + 0.0029·wks2
5th centile −25.6892 + 3.6190·wks 5th centile 0.3354 − 0.0565·wks + 0.0029·wks2
Fronto-occipital diameter (FOD) FL/BPD
Mean −30.9727 + 4.6122·wks Mean 0.9399 − 0.1510·wks + 0.0083·wks2
Head circumference (HC) FL/AC
Mean −90.3529 + 13.4114·wks Mean −0.1360 + 0.0208·wks
5th centile −100.4502 − 13.4114·wks 5th centile −0.1666 + 0.0208·wks
95th centile −80.2556 + 13.4114·wks 95th centile −0.1054 + 0.0208·wks
Cisterna magna (CM) Weight (BPD,AC)
Mean exp(−1.5985 + 0.1749·wks) Mean exp(1.7757 + 0.2122·wks)
5th centile exp(−1.9801 + 0.1749·wks) 5th centile exp(1.6256 + 0.2122·wks)
95th centile exp(−1.2168 + 0.1749·wks) 95th centile exp(1.9259 + 0.2122·wks)
Transcerebellar diameter (TCD)
Mean exp(−9.5418 + 1.7103·wks − 0.0609·wks2)
5th centile exp(−9.7859 + 1.7103·wks – 0.0609·wks2)
95th centile exp(−9.2977 + 1.7103·wks − 0.0609·wks2) below the 5th centile in first-trimester fetuses18. Certain
Anterior cerebral ventricle (Va) transvaginally obtained ratios between BPD and femur and
Mean −5.3349 + 0.7851·wks
humerus lengths, HC and AC and foot length have been
5th centile −6.4276 + 0.7851·wks
95th centile −4.2421 + 0.7851·wks investigated in the first trimester with respect to their useful-
Posterior cerebral ventricle (Vp) ness as markers of aneuploidies19 but only trisomy 13 fetuses
Mean −7.2059 + 0.9360·wks showed abnormal values for HC/ AC, BPD/ HL and BPD/FL,
5th centile −5.8386 + 0.7303·wks and other studies have shown relatively short femur to be of
95th centile −8.5731 + 1.1416·wks
limited use for the detection of trisomy 21 before 18 weeks20.
Hemisphere (HEM)
Mean −11.3596 + 1.6124·wks Early measurements of BPD were also used to predict long
5th centile −12.9822 + 1.6124·wks bone growth in later pregnancy21, and early transvaginal
95th centile −9.7369 + 1.6124·wks diagnosis of skeletal dysplasias has also been attempted using
Abdominal transverse diameter (ATD) FL against CRL and FL against BPD ratios with good predic-
Mean exp(0.6448 + 0.1875·wks)
tion in severe cases22. Our data for FL vs. gestation, FL/CRL,
5th centile exp(0.4833 + 0.1875·wks)
95th centile exp(0.8064 + 0.1875·wks) and FL/ BPD correspond well with those of Gabrielli et al.22.
Abdominal anteroposterior diameter (AAP) The FL/ AC ratio in later pregnancy has also been used in the
Mean −27.5424 + 3.8053·wks prediction of the severity of skeletal dysplasia and a ratio
5th centile −20.0957 + 2.9392·wks < 0.16 resulted in a lethal outcome in all nine cases studied,
95th centile −34.9890 + 4.6714·wks
whereas a ratio ≥ 0.16 resulted in a non-lethal form of skeletal
Abdominal circumference (AC)
Mean −85.0484 + 11.8552·wks dysplasia or in a healthy child23.
5th centile −94.7459 + 11.8552·wks Studies on the crown−chin length have shown that detailed
95th centile −75.3510 + 11.8552·wks first-trimester biometry may help in detecting specific mal-
Femur length (FL) formations such as acrania/anencephaly24.
Mean exp(−2.0220 + 0.3255·wks) In conclusion, the establishment of comprehensive refer-
5th centile exp(−2.9381 + 0.3737·wks)
95th centile exp(−1.1058 + 0.2772·wks)
ence ranges for first-trimester transabdominal fetal biometry
Va/HEM may allow the diagnosis of early onset symmetrical or asym-
Mean 0.5131 metrical intrauterine growth restriction and the interpreta-
5th centile 0.0102 + 0.0307·wks tion of measurements in chromosomally abnormal fetuses
95th centile 1.0159 − 0.0307·wks
and may help in detecting skeletal dysplasias or acrania/anen-
Vp/HEM
Mean exp(−0.6845) cephaly. The use of these biometric measurements in addition
5th centile exp(−1.6418 + 0.0554·wks) to measurement of NT, first-trimester biochemistry, first-
95th centile exp(0.2728 − 0.0554·wks) trimester ductus venosus Doppler sonography and first-
Head circumference/abdominal circumference trimester anomaly scanning may contribute to a total shift
Mean 1.2305
towards first-trimester screening.
5th centile 1.0849
95th centile 1.3760
BPD/FL R EF ER EN C ES
Mean exp(3.1027 − 0.1629·wks)
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