Diagnostic ultrasound ( PDFDrive )

CHAPTER 31 Chromosomal Abnormalities 1095
S
D
IVC
DV
A
UV
A
B
FIG. 31.5 Reversed Flow in Ductus Venosus. (A) Color Doppler anatomy of vessels at oblique sagittal view of fetal trunk. DV, Ductus venosus;
IVC, inferior vena cava; UV, umbilical vein. (B) Abnormal ductus venosus sonogram shows a reversed a wave. Absent or reversed a-wave low
can occur in cardiac failure, with or without cardiac defects, and in chromosomally abnormal fetuses. D, Diastole; S, systole.
with experience, even for competent imagers. It has been recommended
that the nasal bone be considered a contingency marker
in patients whose irst-trimester risk based on NT and biochemistry
is in an intermediate-risk category between 1 in 101 and
1 in 1000. 56,60,61
Other Markers for Aneuploidy
Reversed Flow in Ductus Venosus
he ductus venosus directs well-oxygenated blood from the
umbilical vein to the coronary and cerebral circulation. Abnormal
blood low demonstrated as a reversed a wave in the ductus
venosus is seen in 80% of fetuses with trisomy 21 and in 5% of
euploid fetuses 9,62 (Fig. 31.5).
Tricuspid Regurgitation
Tricuspid regurgitation has also been proposed as a method of
risk assessment. Falcon et al. 63 compared 77 fetuses with trisomy
21 and 232 chromosomally normal fetuses from singleton
pregnancies at 11 to 14 weeks of gestation. Tricuspid regurgitation
was identiied in 57 (74%) of trisomy 21 fetuses and in 16 (7%)
of euploid fetuses. No relationship between tricuspid regurgitation
and the levels of maternal serum free β-hCG and PAPP-A was
identiied. he authors concluded that an integrated sonographic
and biochemical test can identify about 90% of trisomy 21 fetuses
for a 2% to 3% FPR.
First-trimester sonographic screening using NT and maternal
age (without biochemistry) is enhanced by using additional
ultrasound markers of nasal bone, tricuspid and ductus venosus
low. Detection rates of Down syndrome of 80%, 87%, and 94%
are reported when using one, two, or three additional ultrasound
markers while maintaining the FPR at 3%. 64
Thickened Nuchal Translucency With
Normal Karyotype
A thickened NT is associated with an increased risk of structural
fetal anomalies including congenital heart defects (CHDs). In
a study of 29,154 euploid fetuses between 10 to 14 weeks’ gestation,
Hyett et al. 65 identiied 50 with CHDs; 56% of the fetuses were
from a group of 1822 with an NT thickness greater than 95%.
In a meta-analysis evaluating the screening performance of
increased irst-trimester NT for the detection of major CHDs,
eight independent studies with 58,492 patients were reviewed.
An NT greater than 99% had a sensitivity of 30% for the detection
of CHDs. If an NT greater than 99% is used as an indication for
a fetal echocardiogram, 1 in 16 referred cases would have CHDs.
If the threshold was lowered to fetuses with an NT greater than
95%, 1 in 33 referred cases would have a major CHD. 66 Data
from the FASTER trial conirmed that the incidence of major
CHD increased with increasing NT, although the sensitivity for
CHD detection was only 9.6%. hese investigators concluded
that NT lacked the qualities of a good screening test for heart
disease; however, an NT of 2.5 MoM (99%) or greater is considered
an indication for fetal echocardiography. 67 A population-based
study evaluating the performance of a irst-trimester thickened
NT in the detection of critical CHDs in euploid liveborn infants
demonstrated that an NT of greater than 99% had a 5-fold
increased risk while an NT of 3.5 mm or larger had a 12-fold
increased risk compared with fetuses whose NT measured less
than 90% for CRL. 68
Fetuses with a thick NT are at increased risk for a variety of
major congenital abnormalities in addition to CHDs (Fig. 31.6).
In combined data from 28 studies of 6153 euploid fetuses with
thick NT, the prevalence of major anomalies was 7.3% (range,
3%-50%). he prevalence of major anomalies increased from
1.6% in those with an NT less than 95% to 2.5% in those with
an NT 95% to 99%, 10% in those with an NT of 3.5 to 4.4 mm,
and increasing dramatically thereater to 46% in those with an
NT greater than 6.5 mm. 15 Anomalies demonstrated included
facial clets, diaphragmatic hernia, abdominal wall defects as
well as a multitude of other structural abnormalities. Timmerman
et al. demonstrated an increased risk of oral facial clet in
chromosomally normal fetuses with a thick NT. 69 In a large
population-based study of euploid infants examining the relation