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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