Diagnostic ultrasound ( PDFDrive )

1096 PART IV Obstetric and Fetal Sonography
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FIG. 31.6 Structural Abnormalities Seen at the 11- to 14-Week Ultrasound Performed for NT Assessment. (A) Three-dimensional image
of fetus demonstrating an omphalocele. (B) Sagittal scan of a fetus demonstrating an irregular cephalic contour characteristic of anencephaly.
(C) Transverse view of the fetal head demonstrating a monoventricle of alobar holoprosencephaly. Note the septated cystic hygroma. (D) View
of the fetal hand demonstrating polydactyly. (E) Sagittal view of a fetus with a large cystic structure (arrowheads) in the fetal pelvis characteristic
of megacystis. Note that the amniotic luid volume is still normal because of gestational age.
of an increased NT and major noncardiac structural defects, an
NT measurement of 95% or greater or NT of 3.5 mm or larger
was associated with an increased risk compared with those having
an NT less than 90% for CRL. he most commonly identiied
anomalies were hydrocephalus, agenesis/hypoplasia/dysgenesis
of the lung, atresia or stenosis of the small intestine, osteodystrophies,
and diaphragmatic anomalies. In this study, the association
with orofacial clets seen by Timmerman was not noted;
however, the populations studied were quite diferent. 47 A fetus
with a thickened NT should be evaluated for other structural
abnormalities as extensively as possible at the time of the irsttrimester
scan. 70-72 In ongoing pregnancies, a detailed structural
evaluation with meticulous attention to fetal cardiac imaging in
the second trimester is warranted.
In chromosomally normal fetuses, the risk of intrauterine
demise increases with increasing NT. In a study of 6650 pregnancies
undergoing NT screening, the prevalence of miscarriage,
fetal death, or termination for an anomaly was 1.5% in euploid
fetuses with an NT below the 95th percentile compared with
18% in those with an NT above the 99th percentile. 73 Westin
et al. 74 reported on 16,260 euploid fetuses from an unselected
population to determine how well NT measurements predicted
adverse outcome. he overall rate of adverse outcome was 2.7%.
he risk of adverse outcome increased with higher NT measurements.
An NT of 3 mm or greater was associated with a 6-fold
increase in adverse outcome, 3.5 mm or greater with a 15-fold
increased risk, and 4.5 mm or greater with a 30-fold increased
risk. hese authors concluded that likelihood ratios could be
used to calculate an individual’s risk of adverse outcome but
could not reliably distinguish between normal and adverse
outcome.
Not all fetuses with a thick NT have an abnormal outcome.
In 2001, Souka et al. 75 reported on 1320 euploid singleton
pregnancies with an NT of 3.5 mm or greater. hese fetuses
underwent sonographic evaluation at 14 to 16 weeks and 20 to
22 weeks. he chance of a live birth with no defect was 86% in
the group with an NT of 3.5 to 4.4 mm, 77% for NT of 4.5 to
5.4 mm, and 67% for NT of 5.5 to 6.4 mm. In fetuses with an
NT of 6.5 mm or greater, the chance of normal outcome was
31%. In total, there were 200 fetuses (15.5%) with abnormalities,
80% of which were diagnosed prenatally. here were 1080 (82%)
survivors, 60 (6%) of whom had abnormalities requiring medical
or surgical care or were developmentally delayed. In a group of
82 fetuses with persistent nuchal thickening but an otherwise
normal scan, 19% had an adverse outcome. In the group of 980
euploid fetuses with a normal second-trimester scan, there were
22 (2%) with adverse outcome. Severe developmental delay was
seen in 1 in 82 (1%) with isolated persistent nuchal thickening,
compared with 4 in 980 (0.4%) with a normal scan. 75
Bilardo et al. 76 reviewed the outcome of 675 pregnancies with
an increased NT, known karyotype, and known pregnancy
outcome. Of the study group, 451 (67%) had a normal karyotype,
and 19% of these euploid pregnancies had an adverse outcome.
he range of abnormal outcome varied with the degree of NT
thickening, from 8% with NT between the 95% and 3.4 mm to
80% with NT of 6.5 mm or greater. Second-trimester sonography