Normal images in early pregnancy as mentioned

Normal images in early pregnancy
As mentioned previously, to be conservative and to practice with the greatest
safety, only an intrauterine yolk sac, fetal pole, or intrauterine fetal heartbeat
Diagnostic ultrasound 101
First trimester ultrasound

should be identified as an intrauterine pregnancy on bedside ultrasound scans.
The reason for this is that although a gestational sac can be an early marker of a
normal gestation, it can also be the result of hormonal stimulation caused by an
ectopic pregnancy, known as “pseudogestational sac of ectopic pregnancy”
[ 3,13 ]. This finding is seen in up to 10–20% of all ectopic pregnancies [ 13 ].
Therefore, it is not recommended to use this finding as a sign of normal
gestation. The “double decidual sign” has also been described as a reliable
marker for early intrauterine pregnancy ( Figure 4.10 ). This is a sac with
echogenic and hypoechoic rings surrounding it. However, even in the radi-
ology and obstetric literature, there is debate as to the accuracy of this finding,
and it is not present in all cases. Thus, before the appearance of a yolk sac, an
IUP should not be definitively diagnosed by bedside emergency ultrasound.
(A)
(B)
Figure 4.10
Double decidual sign.
The hyperechoic layer
surrounding the
gestational sac can be
seen in both
( A ) longitudinal and
( B ) transverse views.
However, because there
is no yolk sac visualized
within the gestational sac,
this cannot be definitively
called an intrauterine
pregnancy.
102 Diagnostic ultrasound
First trimester ultrasound

When first visible, the gestational sac contains no identifiable structures.
By the time its diameter reaches 5–8 mm, the yolk sac (“sac within the sac”)
should be detectable ( Figure 4.11 ).
By the end of the sixth menstrual week, the mean diameter of the gesta-
tional sac grows by 1 mm/day, the yolk sac appears, and embryonic
cardiac activity may be seen between the yolk sac and the wall of the
chorionic sac even before the embryo is measurable. At this point, the
tiny embryo is surrounded by a small amniotic membrane. This complex,
located between the yolk sac and the chorionic wall, is termed the fetal pole
( Figure 4.12 ).
The embryo grows by about 1 mm/day in crown–rump length, and by
the end of the seventh menstrual week the embryo measures 5–10 mm
(A)
(B)
Figure 4.11
In ( A ), the double
decidual sign is
clearly seen. More
importantly, a yolk
sac is seen in both
( A ) and ( B ). This
“sac within the sac”
(yolk sac) is the first
definitive sign of an
intrauterine
pregnancy.
Diagnostic ultrasound 103
First trimester ultrasound

( Figures 4.13 and 4.14 ) and should exhibit cardiac motion on both transva-
ginal and transabdominal scanning.
The gold standard for the diagnosis of a living intrauterine pregnancy is
the visualization of embryonic cardiac activity. This may be seen as early as
41–43 menstrual days (6 weeks) or when the mean sac diameter is 12–16 mm.