Compléter
First Trimester 6weeks+
1
>7mm
Heart
>4
35
pole
trilaminar
be
>18
Visualization
of
the
embryo
on
ultrasound
is
often
referred
to
as
the
"
fetal
"
and
should
be
seen
with
MSD
mm
.
?
At
beginning
of
fifth
week
,
bilaminar
embryonic
disk
converts
into
(
three
germ
layer
)
embryonic
disk
.
?
Organogenesis
begins
at
this
point
.
(
Organs
start
developing
)
?
is
the
first
organ
to
function
within
embryo
o
Starts
beating
at
approximately
days
(
5
to
5½
weeks
)
o
Embryonic
heartbeat
must
seen
in
living
embryo
when
CRL
mm
.
with
no
heartbeat
is
considered
nonviable
.
2
Ectoderm
5
Mesoderm
Endoderm
3
primitive
germ
cell
layers
that
compromise
embryonic
disk
by
-
week
past
LMP
o
:
inner
layer
-
becomes
GI
&
respiratory
systems
o
:
middle
layer
?
becomes
musculoskeletal
&
circulatory
systems
o
:
outer
layer
?
becomes
brain
&
nervous
system
,
and
ski
n
3
allantois
sixth
Omphalomesenteric
Vitelline
allantoic
trilaminar
2
constriction
gastrointestinal
umbilical
Allantois
At
beginning
of
week
of
gestation
,
embryonic
disk
folds
into
Cshaped
embryo
.
o
While
embryonic
folding
continues
,
this
results
in
a
or
narrowing
between
embryo
and
yolk
sac
,
creating
the
yolk
stalk
?
The
yolk
stalk
consists
of
ducts
:
?
/
duct
:
part
of
the
connecting
stalk
of
the
embryo
that
gives
rise
to
part
of
the
umbilical
cord
and
bladder
.
Obliterates
to
form
the
urachus
.
?
duct
/
duct
:
During
embryonic
folding
,
the
dorsal
aspect
of
yolk
sac
(
vitelline
duct
)
is
incorporated
into
the
embryo
,
developing
the
foregut
,
midgut
,
hindgut
,
and
forming
the
entire
tract
,
liver
,
biliary
tract
,
and
pancreas
o
The
yolk
stalk
and
are
brought
together
by
expanding
amnion
,
which
covers
the
three
structures
forming
the
cord
.
4
ectoderm
Prosencephalon
cystic
Cystic
myelencephalon
parallel
Dandy
Rhombencephalon
8
metencephalon
From
6
to
10
Weeks
:
?
Spine
develops
from
o
May
be
visualized
sonographically
as
echogenic
lines
at
6
weeks
of
gestation
.
?
Cranium
undergoes
dramatic
changes
from
sixth
to
10th
week
of
gestation
o
By
weeks
,
3
vesicles
seen
within
fetal
brain
:
?
?
Mesencephalon
?
-
Divides
into
two
segments
:
?
Cephalic
portion
:
which
forms
cerebellum
and
pons
?
Caudal
component
:
which
forms
the
medulla
o
Once
rhombencephalon
divides
,
the
cystic
rhomboid
fossa
forms
:
a
structure
,
seen
within
posterior
aspect
of
embryonic
cranium
?
This
should
not
be
confused
with
pathology
,
such
as
-
Walker
malformation
.
?
rhomboid
fossa
can
routinely
be
imaged
sonographically
from
eighth
to
10th
week
of
gestation
.
5
medulla
falx
10
CSF
fossa
By
9
weeks
the
midline
is
formed
and
the
echogenic
choroid
plexus
tissue
seen
this
produces
.
The
lateral
ventricles
completely
fill
cerebral
vault
?
At
weeks
further
evolution
of
cerebellum
,
,
and
medulla
oblongata
encloses
rhomboid
to
form
primitive
fourth
ventricle
and
part
of
cerebral
aqueduct
of
Sylvius
.
?
Cerebellum
is
fused
and
brain
structure
complete
shortly
thereafter
6
seventh
10th
calcification
cranial
bony
tail
clavicle
transvaginal
neural
More
6
-
10
weeks
changes
:
o
Limb
buds
and
embryonic
are
recognizable
during
sixth
week
of
gestation
o
Sonographically
,
limb
buds
may
be
detected
from
week
on
.
o
Hands
and
feet
develop
later
in
first
trimester
and
completely
formed
by
end
of
week
of
gestation
o
Fingers
and
toes
have
been
identified
using
sonography
at
10
weeks
o
Limbs
not
routinely
identified
until
of
long
bones
begins
at
10
weeks
o
8
weeks
-
Calcification
of
begins
,
followed
by
ossification
of
mandible
,
palate
,
vertebral
column
,
arches
o
9
weeks
-
Frontal
bones
begin
to
calcify
followed
by
long
bones
o
10
weeks
-
Further
palate
development
may
be
visualized
7
6
external
10
primitive
echogenic
Midgut
omphalocele
12
gastroschisi
elongates
Anterior
abdominal
wall
is
developed
by
weeks
gestation
o
The
gut
is
formed
simultaneously
as
the
dorsal
yolk
sac
is
incorporated
into
the
embryo
.
It
then
develops
into
the
midgut
.
o
forms
the
majority
of
small
bowel
,
cecum
,
ascending
colon
,
proximal
transverse
colon
o
As
amniotic
expansion
occurs
,
midgut
faster
than
embryo
,
causing
midgut
to
herniate
into
the
base
of
umbilical
cord
o
So
because
there
?
s
not
enough
room
in
the
abdomen
for
the
midgut
(
bowel
)
to
grow
at
it
?
s
normal
rate
,
it
grows
and
develops
to
the
fetal
abdomen
and
then
migrates
back
in
when
there
?
s
enough
space
.
?
This
transition
of
bowel
can
readily
be
visualized
as
an
mass
within
base
of
umbilical
cord
.
o
Until
weeks
of
gestation
,
midgut
loop
continues
to
grow
and
rotate
before
it
descends
into
fetal
abdomen
at
about
the
11th
week
.
o
After
weeks
of
gestation
,
this
echogenic
umbilical
cord
mass
is
no
longer
visualized
and
echogenic
bowel
is
now
seen
within
fetal
abdomen
o
It
is
important
that
this
normal
embryologic
event
not
be
confused
with
pathologic
processes
,
such
as
or
8
100
90
maternal
eighth
140
?
By
end
of
week
of
gestation
,
heart
has
obtained
its
adult
configuration
.
o
Embryonic
cardiac
rates
vary
with
gestational
age
.
to
115
bpm
at
6
weeks
,
to
160
bpm
at
9
weeks
.
o
Documenting
fetal
heartbeat
of
over
bpm
provides
discrimination
from
maternal
heartbeat
.
?
If
unsure
of
maternal
vs
fetal
heart
rate
,
or
is
fetal
heart
rate
is
low
,
obtain
and
document
puls
e
9
16
chorioamniotic
placenta
bleb
5½
?
Transvaginally
,
the
amniotic
membrane
that
separates
the
amniotic
cavity
and
chorionic
cavity
is
routinely
seen
after
weeks
?
"
double
sign
"
-
simultaneous
side
by
side
appearance
of
amnion
and
yolk
sac
o
Gradually
,
the
takes
over
process
of
waste
removal
,
amniotic
cavity
expands
,
and
chorionic
cavity
decreases
in
size
.
?
Fusion
of
membranes
(
fusion
)
occurs
at
approximately
14
to
15
weeks
and
should
be
complete
by
week
s
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