Diagnostic ultrasound ( PDFDrive )

CHAPTER 30 The First Trimester 1055
A
B
C D E
FIG. 30.5 Intradecidual Sac Sign at 32 Days. (A) TAS fails to show the gestational sac. (B) TVS shows the echogenic ring of the sac implanted
just below the endometrial stripe. In another woman (C) transverse and (D) sagittal TVS show an early gestational sac (arrow). The sac (arrow)
slightly displaces the endometrial stripe posteriorly and has a slightly echogenic rim, seen best on (E) high-resolution image.
luid. his diference is best appreciated if the system gain is
increased. he low-level echoes within the chorionic luid are
accentuated, and yet the amniotic luid remains echo free 31 (Fig.
30.8). he low-level echoes are likely caused by the relatively
thick proteinaceous material in chorionic luid. 32
Some researchers have investigated using color low Doppler
sonography to help identify the presence of an early IUP. Emerson
et al. 33 found that the detection of peritrophoblastic low of high
velocity and low impedance increased the sensitivity of detection
of IUP from 90% to 99%. Parvey et al. 29 found this low pattern
in only 15% of IUPs without a visible yolk sac or embryo. hey
considered that combining the Doppler indings with the
sonographic identiication of inner chorionic rim would yield a
high sensitivity and speciicity of over 90%. However, this exposes
the early IUP to the increased power deposition of Doppler
scanning (see Chapter 29). herefore Doppler should not be
routinely performed when assessing the early IUP. 34 However,
when scanning in the adnexal region, use of Doppler
and associated power deposition is not a concern, because the
irst-trimester pregnancy (if ectopic) is nonviable (and because
any IUP would be out of the ield of insonation).
β-hCG and Early Pregnancy Ultrasound
Serum hCG levels perform an important complementary role
with ultrasound in the evaluation of early pregnancy. Levels
using the serum beta subunit of human chorionic gonadotropin
(β-hCG) provide a reproducible value that can help guide
management in clinical practice.
A negative serum β-hCG level excludes pregnancy in a young
woman with pain or bleeding. he serum β-hCG test yields
positive results at approximately 23 days of gestational age, 35
before a normal intrauterine gestational sac may be imaged with
TVS. A disproportionately lower than expected β-hCG level is
an indicator of a poor prognosis. 36 he World Health Organization
(WHO) has issued several sets of standards for β-hCG, calibrated
in International Units (IU). Over the years, β-hCG levels have