Nuchal
translucency evaluation a component of
first trimester aneuploidy screening has
had a major impact on the number of pregnancies
receiving late first trimester
ultrasound examination . It represents the maximum thickness of the
subcutaneous translucent area between
the skin and soft tissue overlying the
fetal spone at the back of the neck . It is
measured in the Sagittal plane between 11 and 14 weeks using
precise criteria When the
nuchal translucency is increased the
r4isk for fetal aneuploidy and various structural anomalies – including heart defects-
is significantly elevated.
Aneuploidy screening using nuchal
translucency measurement in conjunctions with assessment of maternal serum human chorionic gonadotropin and pregnancy associated plasma protein
First
Trimester fetal anomaly detection
Assessment for selected fetal abnormalities in an at risk pregnancy7 is another indicatin
for first trimester sonography . Research in this area has focused on antomy visible at 11 to 14 weeks to coincide with sonography performed a
s part of aneuploidy screening / With current
technology it is not realistic to expect that all major
abnormalities detectable in the second
trimester may be visualized inj the first trimester . A study of systematic
anatomy evaluation between 11
and 14 weeks in more than 40,000 pregnancies
yielded a detectin rate of
approximately 40 percent for
nonchromosomal abnormalities .
this detection rate is nearly identical to that from a review of more than 60,000 pregancies
from 15 studies and is also comparable with other reports . Identification varies considerably according to
the specific abnormality .
For example reported detection rates are extremely high for anencephaly alobar holoprosencephaly and ventral wall defects . However
only one third of major cardiac
anomalies have been identified
with no detected cases of microcephaly agenesis of the corpus
callosum cerebellar
abnormalities congenital pulmonary airway malformation or bowel obstruction. Thus as first trimester sonography
is unreliable for detection of many
major abnormalities. It should not
replace second trimester
anatomical evaluation .
Second and Third Trimester Sonography
The
many indications for second and
third trimester sonography
are listed .There are three types
of examinations Standard. Specialized and limited
1 Standard
sonographic examination is the most commonly performed Components ar listed .
The fetal anatomical structusres that should be evaluated during he examination
which are listed . may be adequately assessed
after approximately 18 weeks when examining twins or other multiples documentation also
includes the number of chorions and amnions comparison of fetal
sizes estimation of amnionic fluid
volume within each sac and fetal
sex determination .
There are several types of specialized examination . The targeted examination is a detailed anatomical survey performed when an abnormality is suspected on
the basis of history screening test
result or abnormal findings from s standard examination . A targeted
examination is performed and interpreted by an experienced operator . It includes the anatomical structures listed.
Along with additional views
of the brainadn cranium. Neck profile
lungs and diaphragm cardiac anatomy
live shape and curvature of the
spine hands and feet and any placental abnormalities . the physician performing the
examination further determines whether
other examination components will
be needed on a case by case basis . Other
specialized examinations include fetal echocardiography ad Doppler evaluation
biophysical profile and
additional biometric measurements.
3 A
limited examination is performed
to address a specific clinical question Examples include amniotic fluid
volume assessment placental location or evaluation of fetal presentation or viability . In most cases a limited examination is appropriate only when a prior standard or targeted examination has
previously been performed .
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