Ultrasound in the First Trimester: A Guide to Goals, Appearances and Findings

1
ULTRASOUND IN
FIRST TRIMESTER
Deepa

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Goals of 1st trimester
ultrasound
 Visualisation and localisation of the gestational sac
 Early identification of embryonic demise
 Anembyonic pregnancy
 Identification of embryos still alive but at increased
risk for embryonic/fetal demise
 Determination of number of embryos

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Goals…
 Chorionicity and amnionicity in mutifetal
pregnancy
 Estimation of duration or gestational
age of pregnancy
 Early diagnosis of fetal anomalies and
abnormal embryos

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Sonographic appearance of a
normal intrauterine gestation
 Gestational sac
 Yolk sac
 Embryo and amnion
 Cardiac activity

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Gestational Sac
 Implantation occurs in the fundal region
of the uterus between day 20 and day
23
 At day 23 the entire conceptus
measures 0.1 mm in diameter and cannot
be imaged by TAS or TVS
 Using TVS the size threshold for sac
detection is 2 to 3 mm~4 wks 1 day GA

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 At sonography the tiny GS is perceived as a
small fluid collection surrounded completely
by an echogenic rim of tissue.
 The central collection is the chorionic cavity
and the surrounding echoes are due to
developing chorionic villi and adjacent
decidual tissues
 As the sac enlarges the echogenic rim should
be at least 2 mm thick and its echogenecity
should exceed the level of myometrial echoes

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Intradecidual Sign
 As the sac implants
into the decidualised
endometrium it
should be adjacent
to the linear central
cavity echo complex
without initially
displacing or
distorting it

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Double decidual Sign
As the sac enlarges
it gradually
impresses on and
deforms the central
cavity echo complex
giving rise to the
double decidual sign

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Double decidual sign

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 The normal gestational sac is round in
the very early stages and implants
immediately beneath the thin echogenic
endometrial stripe
 As it enlarges it has a somewhat oval
shape due to pressure exerted by the
muscular uterine walls.
 Can be distorted during TVS

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 Chorionic sac is
weakly reflective
and more echogenic
than the amniotic
fluid
 The cause of the low
level echoes is likely
due to the relatively
thick proteinaceous
material in the
chorionic fluid

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Role of TVCFD
 May be helpful in identifying the presence of an early
IU gestational sac
 Helps in distinguishing a normal from a failed IU
gestation
 Detection of an ectopic pregnancy through exclusion
of an intrauterine pregnancy
 Detection of peritrophoblastic flow of high velocity
and low impedence:sensitivity of 90-99%

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Yolk Sac
 FIRST STRUCTURE TO BE SEEN WITHIN
THE G.SAC
 ALWAYS SEEN WHEN
MSD > 8mm TVS
MSD > 20mm TAS
 DETERMINES THE AMNIOCITY OF PREGNANCY

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 Demonstration of a yolk sac helpful in
differentiating an early intrauterine gestation
from a decidual cast.
 The upper limit of normal for yolk sac
diameter between 5 and 10 wks of MA is
5.6mm.
 Functions
Transfer of nutrients
Angiogenesis
Haematopoesis

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AMNION
DOUBLE BLEB SIGN
YOLK SAC AMNION
 SEEN AS EARLY AS 5.5 WEEKS WHEN CRL is 2mm
 EMBRYONIC DISK LIES BETWEEN TWO BLEBS

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 Amniotic fluid is a colorless,dermal exudate
initially
 It becomes pale yellow as the skin cornifies
and kidneys begin to function about 11 weeks
 The amnion is barely visible at 6 weeks
 The cavity becomes more spherical at 7 weeks
 The amniotic cavity expands and fills the
chorionic cavity completely by week 14 to 16.

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Early embryo and cardiac activity
 Cardiac activity can be identified as early as
34 days at a CRL of 1 to 2 mm
 During the first TM, cardiac rates vary with
GA
 At 6 weeks the rate is relatively slow:
typically b/n 100 and 115 BPM
 It increases rapidly and by 8 weeks is b/n 144
and 159 BPM.
 After 9 weeks the rate plateaus at 137 to
144 BPM

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Fetal heart rate before 6 weeks

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ESTIMATION OF
GESTATIONAL AGE

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ESTIMATION OF
GESTATIONAL AGE
 MEAN GESTATIONAL SAC
DIAMETER
 CROWN RUMP LENGTH
 BPD,FL,HC & AC

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MSD
 The first structure that can be measured for
calculating GA is the GS
 Sac measurements should be obtained if no yolk sac
or embryo is visible
 To maintain uniformity GS size should be determined
by calculating the MSD
 This value is obtained by adding the three orthogonal
dimensions of the chorionic cavity and dividing by 3

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CRL
 Most accurate method of dating pregnancy
between 6 and 12 weeks
 When the embryonic disk is detected initially
at 6 weeks GA, it may be too small to actually
measure
 Later it becomes possible to measure the
embryonic disk but cannot distinguish crown
from rump.

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BPD,HC,AC,FL
 By the end of first trimester,
measurement of BPD becomes more
accurate than the CRL
 The menstrual age of pregnancy is
established in the 1st TM

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G.SAC CRITERIA FOR POOR
OUTCOME
TAS
 MSD>25mm BUT NO EMBRYO
 MSD>20mm BUT NO YOLK SAC
TVS
 MSD>16mm BUT NO EMBRYO
 MSD>8mm BUT NO YOLK SAC

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Other criteria….
 DISTORTED SAC SHAPE
 THIN TROPHOBLASTIC REACTION
(<2mm)
 ABNORMALLY LOW PLACED G.SAC

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YOLK SAC CRITERIA FOR
POOR OUTCOME
 SAC DIAMETER > 6mm
 THIN ASYMMETRIC Y.SAC
 CALCIFIED OR ECHOGENIC Y.SAC
 SAC DIAMETER < 2mm

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CRITERIA FOR ABNORMAL
AMNION
 VISUALISATION OF THE AMNION IN THE
ABSENCE OF EMBRYO AFTER 7 WEEKS
INDICATES
 Anembryonic pregnancy
 Embryonic demise
 A LARGER THAN NORMAL OR FLOPPY
AMNIOTIC SAC
 COLLAPSED IRREGULAR AMNION

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EMBRYONIC CARDIAC
ACTIVITY
SINGLE MOSTIMPORTANTFEATURE FOR CONFIRMATION OF
FETALLIFE
DETECTEDAT 6 WKS
ABSENT CARDIAC ACTIVITY+BLEEDINGPV 100% EMBRYONIC
MORTALITY
ABSENT CARDIAC ACTIVITY +SUBCHORIONICHAEMORRHAGE-
88% MORTALITY

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EMBRYONIC
BRADYCARDIA
INDICATES IMPENDING DEMISE
CRL HR
<5mm <80 bpm
5-10mm <100bpm
>10mm <110 bpm

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Embryonic Bradycardia

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FIRST TRIMESTER
BLEEDING

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FIRST TRIMESTER
BLEEDING
 ABORTIONS
 ECTOPIC PREGNANCY
 BLIGHTED OVUM
 INTRASAC PERISAC BLEEDING
 HYDATIDIFORM MOLE
 VANISHING TWIN

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ABORTION
 EXPULSION OF THE DEAD PRODUCTS
OF CONCEPTION BEFORE 24 WKS OF
GESTATION
 Types
1.THREATENED ABORTION
2 .INCOMPLETE
3 .COMPLETE
4. INEVITABLE
5. MISSED ABORTION
6. SEPTIC ABORTION

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THREATENED ABORTION
 VIABLE FETUS WITH BLEEDING PV
OCCURING IN FIRST 20 WKS OF
GESTATION WITH CLOSED CERVIX
 NOT VISIBLE SONOGRAPHICALLY
 SERIAL SONOGRAM IS NECESSARY

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INCOMPLETE ABORTION
PARTIAL EVACAUTION OF FETUS AND PLACENTA
WITH SOME RETAINED PORTIONS OF THE
FETUS.
SONOGRAPHICALLY
 ENLARGED UTERUS
 EMPTY ILL DEFINED G.SAC
 SAC WITH INTERNAL ECHOES
 NO SAC
 LARGE CLUMPS OF ECHOES

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Incomplete abortion

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COMPLETE ABORTION
 COMPLETE EXPULSION OF THE PRODUCTS.
UTERUS CONTRACTS AND BLEEDING
STOPS.
SONOGRAPHICALLY
 ENLARGED UTERUS
 G.SAC OR FETAL POLE NOT IDENTIFIED
 PROMINENT THICKENING OF THE
CENTRAL CAVITY INTERFACE-Represents
decidual reaction

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INEVITABLE ABORTION
 ABORTION IN PROGRESS
SONOGRAPHICALLY
 CERVIX DILATED
 SONOLUCENT SPACE SEEN AROUND SAC
 FLUID - FLUID LEVEL
 G.SAC SEEN AT THE LEVEL OF CERVIX

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Inevitable Abortion

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MISSED ABORTION
 RETENTION OF THE DEAD FETUS WITHIN THE
UTERUS
sonographically
 UT SMALL FOR DATES
 EARLY MISSED ABORTION - G.SAC CONTAINS
F.POLE ,NO CARDIAC ACTIVITY

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SEPTIC ABORTION
 INFECTED PRODUCTS OF CONCEPTION AS
A RESULT OF SURGICAL ABORTION WITH
NON-STERILE DEVICES
USG
 UT ENLARGED
 SHADOWING (due to gas forming
organisms/retained bony fragments)
 FLUID IN THE POD
 UTERUS PERFORATION OCCURS

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ECTOPIC PREGNANCY
 IMPLANTATION OF THE OVUM OUTSIDE THE
UTERINE CAVITY.
 INCIDENCE 1.4% MORTALITY 15%
 RISK FACTORS:
TUBAL SURGERY,STERILISATION,
DOCUMENTEDTUBAL PATHOLOGY, IUCD,
INFERTILITY
 INCREASED INCIDENCE OF ECTOPICS IN
ARTIFICIAL REPRODUCTION

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Sites of ectopic pregnancy

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Sonographic Findings
 SPECIFIC FEATURE
 LIVEEMBRYOIN THEADNEXA
 NON SPECIFIC FEATURES (CORRELATE WITH BETA
HCG).
 EMPTY UTERUS
 PSEUDOGESTATIONAL SAC
 PARTICULATEASCITES
 ADNEXAL MASS
 ECTOPICTUBALRING
 LOCAL TENDERNESS
 NON-SUPPORTIVE FEATURES
 LIVEINTRAUTERINEPREGNANCY

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True GS vs PseudoGS

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 Local Tenderness: The probe is used to
apply light pressure on the mass. This almost
always elicits a sense of pain but this can
occur in other inflammatory or expanding
masses such as haemorrhagic corpus luteum
 Ectopic Tubal Ring: Concentric ring created
by the trophoblast of the ectopic pregnancy
surrounding the chorionic sac. This ring is
usually within a haematoma that may be
confined to the fallopian tube or may extend
outside it

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 Endovaginal
sonogram shows a
color Doppler image
of the adnexa with
the ring-of-fire
sign. Marked
hyperemia is present
throughout the wall
of an enlarged
fallopian tube.

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Interstitial pregnancy
 Occurs in the intramural portion of the
tube where it traverses the wall of the
uterus to enter the endometrial canal
 Interstitial line sign: Thin echogenic
line extending from the endometrial
canal upto the cornual sac

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Interstitial line sign

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BLIGHTED OVUM
 G.SAC WITH ANEMBRYONIC
GESTATION
USG
 TROPHOBLASTIC RING IN THE UTERUS
 NO FETAL POLE
 SAC WILL NOT INCREASE IN SIZE
 DISCREPANCY B/W SAC SIZE AND
UTERUS SIZE

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FLUID-FLUID LEVEL
DEFINITIVE OF
FETAL DEATH
CRITERIA IN TAS
MSD>25mm – NO FETUS
MSD>20mm – NO Y.SAC
CRITERIA IN TVS
MSD>16mm-NO FETUS
MSD>8mm-NO Y.S
BLIGHTED OVUM

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INTRA AND PERISAC
BLEEDING
 BLEEDING WITHIN THE AMNIOTIC SAC
ADJACENT TO FETUS
 B/W AMNION AND CHORION

 SUBCHORIONIC
 B/W G.SAC AND DECIDUAL REACTION
SITES

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SUBCHORIONIC
HAEMORRHAGE
 CONTIGUOUS WITH
PLACENTA
 ASSOCIATED WITH
50% FETAL LOSS
 SMALL OR MEDIUM
SIZE HAVE BETTER
PROGNOSIS ( < HALF OF
SAC CIRCUMFERENCE )

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Hydatidiform Mole
 Risk Factors :
 Advancing maternal age
 Prior h/o molar pregnancy
 Asian ancestry
 Increased paternal age
 Can be partial or complete
 1. A complete molar pregnancy :occurs when a sperm fertilizes an
empty ovum, resulting in the development of only placental parts. A
complete mole is completely paternal in origin, with a karyotype of
usually 46 XX.
2. A partial mole results when two sperms fertilize a single ovum
results in development of certain or all fetal parts.
predominantly has a triploid karyotype of 69XXX or 69 XXY:

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Symptoms
 Vaginal bleeding,
 Hyperemesis,
 Passage of grape like vesicles per vagina
 Uterus larger than dates
With the advent of high-resolution transvaginal
ultrasound imaging, molar pregnancy is now being
diagnosed at a much earlier stage before all the
classical symptoms develop.
partial molar pregnancy:
 usually asymptomatic
 may present with symptoms of a missed or incomplete abortion.

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 Spectral waveform analysis in a case
of gestational trophoblastic neoplasm
The spectral waveform within the
cystic mass in the uterus reveals a
mixed arterial and venous waveform,
with low resistance arterial flow.

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First Trimester masses
 Ovarian masses:
 Most common is corpus luteum cyst.
 It forms in the secretory phase of the
menstrual cycle and increases in size if
pregnancy occurs.
 Usually <5 cm
 Thin walled unilocular cyst.
 Regress or decrease in size at 16 to 18

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Haemorrhagic corpus luteum cyst at 6wks
gestation

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 Uterine masses:
 Are often associated with localised pain and
tenderness.
 Differentiated from focal myometrial
contractions by the transient nature of
myometrial contractions.A repeat examination
20 to 30 minutes later will reveal
disappearance of the focal contraction while
fibroids persist.

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SCREENIG STRATEGY IN
FIRST TRIMESTER

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Nuchal translucency
Nasal bone
Flow in ductus venosus
Biochemical markers

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Nuchal Translucency
 The appearance of lucency in the neck has
been used in the diagnosis of fetal aneuploidy.
 Septated lucency in women younger than 35
yrs had the greatest risk for aneuploidy
 Increased NT in the presence of normal
chromosomes is associated with
 Cardiac Septal Defects
 Diaphragmatic hernia
 Renal Anomalies
 Abdominal wall defects
 Hypokinesia syndromes

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Normal NT at 12 -13 wks.

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Trisomy 21  NT > 3 mm

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 NT in Trisomy 18

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Other markers - Nasal bone

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Absence of nasal bone

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Other markers
 Flow in ductus venosus:
Three waves-s wave(ventricular systole)
d wave(ventricular diastole)
a wave(atrial contraction)
It is possible to assess ductus venosus blood
flow by TAS and TVS
A right ventral midsagittal plane of the fetal
trunk is obtained and the pulsed doppler gate
is placed in the distal portion of the umbilical
sinus

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Other markers -
Biochemical
 Free  HCG
 Pregnancy Associated Plasma Protein A
( PAPPA)

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Structural Anomalies in
First Trimester

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Physiological Herniation

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CNS Defects
 By 8 weeks the brain cavities appear as
large cystic spaces within the head(on
TVS)
 Choroid plexus becomes visible from 8
weeks and undergoes rapid growth.
 By 10 wks the falx cerebri appear to
divide the midline and the cerebellum
can be seen.

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 The onset of ossification 0f the cranial vault is at 10
weeks gestation
 The development of the corpus callosum begins at 12
to 13 wks
 The ratio of ventricles to cerebral hemisphere is
greater in the first TM as compared to the second.
 At 12 weeks the posterior horn/hemisphere ratio ~
0.6 and a small rim of cerebral cortex appears
surrounding the lateral ventricles.At this stage the
choroid plexus is echogenic and fills all but the
frontal horns of the lateral ventricle.

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 ACRANIA: Absence of membranous
portion of the bone. Only a thin layer
covers the brain. An abnormally shaped
cephalic pole seen on ultrasound .The
base of cranium and orbits are normal
 EXENCEPHALY: Large portion of the
brain is present, but the covering
membrane is no longer visible.

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Anencephaly
 Incidence:1 in 1000 births
 Characterised by absence of cranial vault, cerebral
hemispheres and the diencephalic stuctures and
their replacement by a flattened amorphous vascular
neural mass (area cerebrovasculosa)
 In all cases there is absence of normally formed skin,
cranial bones and brain superior to orbits
 Using TVS,sonographic visible ossification of frontal
bones is not apparent until 11.5 wks and therefore
should not be diagnosed before this age

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Anencephaly
Longitudinal scan at
12 wks showing
absence of
ossification of the
skull and an irregular
outline of the cranial
pole

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Ossification of the
face and orbits looks
like Frog’s eyes due
to failure of
ossification of the
membraous bones of
skull above the orbit

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Absence of cranial
vault in transverse
view

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Coronal section of
the head in 1st TM

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Encephalocele
 A bony defect in the skull, usually
midline ,with accompanying protrusion of
intracranial contents.
 Occipital (75%)
 Frontal (13%)
 Parietal (12%)
 Rare sites:
base of skull,orbits,nose,mouth

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Skull defect in the
occipital bone and
protrusion of
contents at 12 weeks
GA

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Holoprosencephaly
Arises from incomplete cleavage of
forebrain.
The cerebral hemispheres become
visible on USG from 7 wks ,so the
abnormality could theoretically be
diagnosed from this time, but this may
not be always possible.

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 Alobar type: Lack of midline division of the brain
anteriorly by the falx,prominent,fused
thalami,crescent shaped frontal cortex along with
facial anomalies(cyclopia/median cleft lip)
 Semilobar type :Posterior partial separation of
the two hemispheres and ventricles,with incomplete
fusion of the thalami
 Lobar type :Subtle diagnosis on ultrasound with
absence of septum pellucidum as the only feature.

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HOLOPROSENCEPHALY

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Spine
 The spine will be seen as two echogenic parallel lines
from 7 weeks of GA on TVS
 TVS allows visualisation of ossification centres two
weeks earlier than TAS
 The 3 ossification centres are present from 9 wks
may be seen on TVS as small areas slightly more
echogenic than the surrounding tissues
 Ossification of the spine should be seen clearly in the
cervical vertebrae at 11 weeks and echogenicity
gradually down the spine until the lumbosacral region
is visualised at 13 weeks.

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 The neural tube normally closes by 6
weeks and failure of this process
results in spina bifida.
 Cranial findings are
Lemon sign
Small BPD
Ventriculomegaly with hanging choroid plexus
Banana Sign

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Respiratory System
 The diaphragm is formed and the
pleuroperitoneal cavity divides by 9 wks
gestation
 Normal lungs seen in the chest surrounding
the heart at 11weeks
 The left lung lies behind the heart and is
smaller than the right lung
 Echogenicity > liver and =bowel

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 CDH:
If there is a defect in the diaphragm, the abdominal
contents may herniate into the chest from around 10
to 12 wks of gestation. This occurs after the
intestines return to the abdominal cavity from the
umbilical cord
Associated chromosomal defects:
Trisomy 21,Trisomy 18 and Trisomy 13

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GIT
 Account for 15% of congenital abnormalities identifiable by
ultrasound.
 The physiological herniation of midgut into the
umbilical cord is a normal feature of intestinal development,
leading to elongation and rotation of the bowel.
 Week 7: Initial sign of herniation of the gut seen as a
thickening of the cord containing a slight echogenic area at the
abdominal insertion.
 8 Weeks 3 days- 10 weeks 4 days: herniation
occurs
 10 weeks 4 days -11 weeks 5 days: gut
retractedinto the abdominal cavity.
 Stomach seen as a small hypoechoic area on the left side of the
abdomen from 8th week onwards

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Longitudinal view at 10
weeks 5 days showing
physiological herniation

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Transverse view of
the abdomen at 13
wks with a normally
positioned stomach
on the left.The spine
and ribs are seen in
cross section.

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OMPHALOCEOLE
 Sac formed by peritoneum & amnion
 Various abd viscera (usually liver) herniate into
sac
 Location – midline
 Cord insertion into apex of defect
 Usually assosiated with chromosomal anomaly &
extra GI anomaly

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Omphalocele – 11 wks

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GASTROSCHISIS
 Para umbilical abdominal wall defect (right
side)
 Fetal intestine herniate into amniotic cavity
 No covering membrane seen as in
omphaloceole
 Diagnosis possible from 9 wks if free floating
intestines are visualised
 Cord insertion is normal
 Chromosomal anomalies nil

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Genitourinary System
The fetal kidneys have attained their adult form and position by 12 wks
Initially they appear as oval structures in the posterior mid abdomen on
both sides of the fetal spine on transverse plane
In the longitudinal axis they appear along the paravertebral plane of
the spine.
Recently TVS has enabled earlier and more detailed visualization ,as
early as 10 wks.
Its echogenicity is similar to that of fetal lungs in first trimester.
Not possible to differentiate normal structures of kidney,like cortex
and pelvis

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Coronal view of
abdomen showing
kidneys at 12 wks

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 The normal fetal urinary bladder is identified by TAS
from as early as 10 weeks as a spherical hypoechoic
mass within the centre of the fetal pelvis.
 There is a significant increase in bladder length with
CRL, but at 10 to 14 wks, the longitudinal diameter of
the bladder is always <6mm.
 Visualization of the bladder is made easy by the
identification of the intra abdominal portion of the
umbilical arteries using colour doppler.
 It is essential to differentiate bladder from other
cystic lesions of the pelvis

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Fetus at 11 weeks

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Renal Agenesis
 Amniotic fluid in the first trimester is
predorminantly a filtrate of fetal blood
across the skin.
 Fetal urine production begins at 11 to 13 wks
and around this time the fetal skin starts to
keratinise.
 Therefore from 13 to 20 wks there is a
gradual change in the amniotic fluid
component from fetal filtrate to urine.
 Hence oligohydramnios is not seen before 16
weeks

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 The diagnosis of renal agenesis depends
on the inability to see a kidney or
bladder in the first TM
 Doppler study of renal arteries also help
 Adrenals appear as hypoechoic masses
mass of discoid shape,which lies flat in
the renal bed.This can mimic kidneys
and are better differentiated in the
first TM

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Infantile polycystic Kidneys
 Bilaterally enlarged, homogenously echogenic
kidneys.
 Cysts may be difficult to identify.
 May be part of Meckel Gruber Syndrome.
 Usually detected in the second TM.

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Multicystic dysplastic
Kidneys
 The nephrons and collecting tubules are
dysplastic
 Unilateral/bilateral/segmental
 Kidneys are large and multicystic in
early stages.Later becomes small and
echogenic
 The cysts are of varying sizes and have
septae between them.

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Renal Pelvic Dilation
RPD in first TM is AP diameter of
pelvis>3mm

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Megacystis
The longitudinal diameter of normal bladder is
6mm in the 1st TM.
Bladder diameter to CRL ratio<10%
Causes:
PUV in males
Cloacal Anomaly in females
Urethral atresia
Megacystis microcolon intestinal hypoperistalsis
syndrome

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TAS of a 12 wk fetus

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Musculoskeletal System
 Small limb buds of low echogenecity are seen
from 7 wks gestation
 By 9 weeks, fingers and toes are detectable
 From 10 wks, limbs elongate and typical
posture of the foetus appears
 By 11 wks, the limb bones appear to ossify and
all the long bones are consistently seen.

19/06/07 136
 The normal lengths of humerus, radius,
ulna,femur,tibia and fibula are similar at 11 to
14 wks
 Increase linearly with gestation from around
6mm at 11 weeks to 13mm at 14 weeks.
 By 11 wks the foot position in relation to tibia
and fibula is well established.
 Spine ossifies by 11 weeks, skull by 12 weeks
ribs by 13 wks

19/06/07 137
Normal Hands at 12 weeks

19/06/07 138
Skeletal Dysplasias
 Heterogeneous group of disorders of
bone maldevelopment resulting in
abnormal growth and shape of the fetal
skeleton.
 Findings are:
Disproportion between the body and limb length
Lack of limb movements
Failure of ossification of limbs and vertebra
Skin edema

19/06/07 139
Fetal Akinesia Deformation Sequence
 Heterogeous group of conditions resulting in
multiple joint contractures, and fixed flexion
or extension deformities of the
hips,knees,elbows and wrists.
 The sequence includes Congenital lethal
arthrogryposis,multiple pterygium, and pena Shokier
syndromes.
 Diagnosed in the 2nd and 3rd TM.
 Associated with increased NT.

19/06/07 140
Talipes Equinovrus
 Foot adducted and
plantar flexed in the
sagittal and coronal
planes.
 Earliest diagnosis at
13 wks
 Metatarsal long axis
is in the same plane
as the tibia and
fibula

19/06/07 141
Conclusion
 It is now possible to examine the fetal
anatomy in the first TM.
 Certain abnormalities are visualised as
early as 9 wks.
 The optimal GA to visualize fetal anatomy
is at 12-13 wks(by both TAS and TVS).

19/06/07 142
Protocol for first TM scan in
a low risk group
CNS:
Obtain BPD view
Normal skull outline
Presence of falx cerebri
2 choroid plexus
Face:
Profile
Transverse view(orbit and face)
Fetal neck:
Measure NT
Heart:
Fetal heart rate and rhythm
Situs
Axis
Four chamber view
Thorax:
Location of stomach
GIT:
Stomach
Physiologic herniation upto 11 wks+5d
but should not contain liver
GUT:
Bladder<7mm
Musculoskeletal
system:
4 limbs
2 hands and 2 feet

19/06/07 143
The concept of a first TM scan to
solely confirm viability or date the
pregnancy should be abandoned and
an attempt should be made to
visualize the fetal anatomy

Ultrasound in the First Trimester: A Guide to Goals, Appearances and Findings

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Ultrasound in the First Trimester: A Guide to Goals, Appearances and Findings