1M - Fetal Imaging Flashcards
Upon ultrasound, the results show an 80mm fetus with identifiable features and internal organs. What trimester is the fetus in?
1st trimester
What is the first sign of early pregnancy on ultrasound?
Gestational sac
When can we first see the gestational sac?
3-5 weeks gestation
The mean sac diameter is 2-3mm
Where can we see the true gestational sac and the pseudo gestational sac?
True gestational sac can be seen in the eccentrically in the endometrium while the pseudo gestational sac can be seen centrally within the uterine cavity
at 4.5-5 weeks, what is most helpful sign of pregnancy sonographically?
Double decidual sign
What is the possible hcg levels within the first 5 weeks of pregnancy that coincides with the presence of gestational sac?
1000-2000 IU/L
A sonographic
measurement of the gestational sac which is usually
first seen at around 3 weeks after conception (5 weeks
after the last menstrual period), when it measures 2-3
mm
Mean sac diameter
What measurement of MSD with absent fetal pole is indicative of pregnancy failure or missed miscarriage?
> 25mm
What measurement of MSD is suspicious of pregnancy failure if an embryo is not found?
16-24mm
What measure of MSD should yolk sac be already visible?
8mm
First anatomical structure identified within the gestational sac?
Yolk sac
This structure play a critical role in embryonal development by providing nutrients and serving as the site of initial hematopoiesis?
Yolk sac
This is characterized a a structure with a round bright ring measuring <6mm sonographically
Yolk sac
When does the yolk sac involute?
At 11 weeks
When does the yolk sac become unidentfiable?
at 14-20 weeks
Appears as a circular thick-walled echogenic structure
with an anechoic center within the gestational sac, but outside the amniotic membrane
Yolk sac
This is the first direct imaging manifestation of the fetus? Seen as a thickening on the margin of the yolk sac
during early pregnancy. It is often used
synonymously with the term “embryo”.
Fetal pole
When can we first identify the fetal pole?
6.5 weeks with TAS
6 weeks with TVS
Upon TVS what is the MSD if the fetal pole already present?
> or = 16mm
TAS - > or = 25mm
When a fetal pole measures > or = 5mm what what other thing should be detected?
fetal heartbeat
it is the length of the
embryo or fetus from the top of its head to bottom of
torso?
Crown rump length
the largest dimension of the embryo excluding the yolk sac and extremities
It is the most accurate estimation of gestational age in early pregnancy?
Crown rump length
This is due to the small biological variability
This is the primary measure of gestational age from 7-13 weeks?
Crown rump length
accurate to within 5-7 days
What measure of CRL should cardiac activity be present?
7mm
What is the definitive sign of intrauterine pregnancy at 5 weeks?
Gestational sac and yolk sac
if the yolk sac or embryo is not yet visualized, what can be an alternative sign of intrauterine pregnancy?
Double decidual sign
What are the outer and inner parts of the double decidual sign?
Outer - decidua
Inner - chorion
seen as round oval fluid filled collection surrounded by 2 echogenic rings
Visualization of a gestational sac containing a yolk
sac and amniotic sac giving an appearance of two
small bubbles where the embryonic disc is located between the 2 bubbles?
Double bleb sign
How many days of gestation should we first see intradecidual sign and when is the last discriminatory day of gestation should it start be seen to confirm intrauterine pregnancy?
Should be seen at 24 days (threshold level) but not later than 47 days (discriminatory level) to confirm intrauterine pregnancy
This is a frequent cause of first and second trimester hemorrhage caused by blood collecting between the uterine wall and the chorionic membrane
sub chorionic hemorrhage
This is the normal fluid-filled
subcutaneous space identified at the back of the
fetal neck during the late first trimester and early
second trimester (11 weeks 3 days to 13 weeks 6
days).
Nuchal transluency
nuchal fold - seen at second trimester
What does increase in nuchal translucency indicate?
dilated lymphatic vessels and fetal abnormalities
When do we check for nuchal translucency?
11-13 weeks
What are the 3 factors used to calculate for risk of trisomies?
Nuchal translucency
Crown rump length
fetal heart rate
Most accurately reflects gestational age, with a
variation of 7 to 10 days in the second trimester
bi parietal diameter
measurement of the shape of the fetal head
What view is needed to see the biparietal diameter?
Axial view at the level of the thalamus
How to measure biparietal diameter?
From the outer edge of the near cranium to the inner edge of the far cranium
What is the condition if BPD is high for gestational age?
Brachycephaly
What is the condition if BPD is low for gestational age?
dolicocephaly
To correctly measure the head circumference and biparietal diameter, what structures must be included?
cavum septum pellucidum, thalamus, and choroid plexus in the atrium of the lateral ventricles
What measurements reflects growth of the fetal brain?
Head circumference and biparietal diameter
This is a perimeter measurement of the fetal cranium excluding subcutaneous soft tissues.
Head circumference
This measurement reflects the growth of intraabdominal organs and fetal weight and sized? It is the peripheral measurement of the fetal abdomen including the subcutaneous tissue
Abdominal circumference
What are the landmarks in measuring the abdominal circumference?
Portal section of the UV
Stomach
Spine
Serves to monitor growth of long bones?
Femur length
The normal growth and development of the fetus are dependent upon the normal function and integrity of this structure?
Placenta
When can the placenta be first visualized sonographically by TVS
8 weeks
as a focal thickening along the periphery of the gestational sac
evident by 12 weeks
This protects the fetus from injury and allows growth and fetal movement. This is also essential for lung maturation.
Amniotic fluid
This measure the vertical height of the deepest fluid pocket in 4 quadrants?
amniotic fluid index
What is the normal range for amniotic fluid index?
5-20 cms
If AFI is below 5 cms, what is the condition?
Oligohydramnios
What are the causes of oligohydramnios?
Post term
PROM
IUGR
urinary tract abnormalities
If AFI is more than 20 cms, what is the condition?
polyhydramnios
What are the causes of polyhydramnios?
Gestational diabetes - most common
GI and CNS abnormalities
lethal skeletal dysplasia
chromosomal abnormalities
