Diagnostic ultrasound ( PDFDrive )

CHAPTER 28 Overview of Obstetric Imaging 1019
A
B
FIG. 28.4 Multiple Gestations. The entire gestational sac should be examined to identify multiple gestations. (A) Transabdominal image of
diamniotic dichorionic twins. Note the thick, dividing membrane that separates twin A (A), the presenting twin, from twin B (B). (B) Transvaginal
image of diamniotic monochorionic twins at 8 weeks’ gestational age (calipers denote crown rump length [CRL]) with two thin membranes
(arrows, amnion) still close to embryonic poles.
A
B
FIG. 28.5 Anencephaly. (A) Sagittal ultrasound at 10 weeks’ gestation. (B) Sagittal ultrasound in a different fetus at 12 weeks’ gestation. Note
the orbits (arrow) with absent ossiied cranium above this level with angiomatous stroma. The calipers mark the estimate of the crown rump length,
made dificult due to angiomatous stroma above the orbits.
to visualize completely early in the second trimester, particularly
the heart, cardiac outlow tracts, posterior fossa, and
distal spine.
Second and Third Trimesters
he current ACR/AIUM guidelines for the performance of the
second- and third-trimester obstetric ultrasound examinations
describe the standard sonographic examination. 5 It is important
to understand that the guidelines were written to maximize
detection of many fetal abnormalities but are not expected to
allow for detection of all structural abnormalities.
he terminology level I and level II examinations refer to
“standard” or “routine” (level I) and “high risk,” “specialized,” or
“detailed” (level II) obstetric ultrasound. he concept of these