First trimester scan

DR SHILPEN GONDALIA
MD(Obst and Gyn)
Fetal medicine
specialist
Gynec laparoscopic
surgeon
RAJKOT
18 March 2015 Dr Shilpen Gondalia

FIRST TRIMESTER SCREENING
Screening for T21 and other
chromosomal defects
Early anatomic evaluation
Diagnosis of multiple gestation and
defining chorionicity and amnionicity
Prediction of preeclampsia

Screening for chromosomal defects
Maternal age
Nuchal translucency
Fetal heart rate
Serum Biochemistry
New Ultrasound markers

Priori risk
Every women has risk of baby being
affected by chromosomal defect ,,,Priori
Risk
Priori risk is dependent on maternal age
and gestation
The Individual patient specific risk is
calculated by multiplying priori risk with
series of Likely hood ratios

Likely hood ratio
LR for a given Sonographic or
Biochemical measurement is calculated
by dividing the percentage of
chromosomally abnormal fetuses with
normal fetuses with that measurement
Every time a test is carried out the priori
risk is multiplied by LR of the test to
calculate a new risk, which than
becomes priori risk for next test

FIRST TRIMESTER SCAN
Shift in the thinking, From 18-20
wks to 11-14 wks
Better equipments available,
Better understanding of
Embryology
Avoid late terminations

TECHNIQUE FOR NT
CRL 45-84 mm
Neutral position, away from amnion
Zoom the image such that Fetal
head and Upper thorax occupy whole
screen
Zygoma must not be seen
Take largest measurement
Transverse bar of the caliper should
be on white line.

CRL

MIDSAGITTAL

NORMAL NT

INCREASED NT

PATHOPHYSIOLOGY
Cardiac defects/dysfunction
Venous congestion in head and
neck
Altered composition of
extracellular matrix
Failure of lymphatic drainage
Fetal anemia,Hypoproteinamia
Fetal infection

INCREASED NT
With normal karyotype,,majority
will be having normal outcome
Larger the NT worse the
prognosis
Fetal echo and detailed anatomic
evaluation is recommended

INCREASED NT
COMMON in:-
Trisomy 21: Absent NB,AVSD
Trisomy 18:Omphelocele,CHD,MSK,
IUGR
Trisomy 13:Holoprosencephaly,CHD
Omphelocele
Turner(XO):Largest NT to Hydrops
CHDs:24x increased risk
Syndromes:MSK dysplasias,,,so
many

CYSTIC HYGROMA AND HYDROPS
FETALIS
Cystic Hygroma: 50% Aneuploidy
T 21,,XO,,T18
Occurs in 90% of Turners
50 % Euploid: 50 % ll be having
major structural fetal malformations
Cardiac is commonest
Hydrops: Generalized subcutaneous
thickening +/- ascites effusions,A
wave reversal in DV,TR

10 WKS
CYSTIC HYGROMA AXIAL

12 WKS
CORONAL SAGITTAL

FETAL HEART RATE
In normal pregnancy,
FHR increases from
110 bpm at 5 wks to
170 at 10 wks and than
gradually decreases to
150 bpm by 14wks

FHR
Trisomy 21: FHR is mildly increased and
is above 95th centile in 15% of cases
Trisomy 18: FHR is mildly decreased and
is below 5th centile in 15% of cases
Trisomy 13:FHR is markedly increased
and is above 95th centile in 85% of
fetuses

SERUM BIOCHEMISTRY
Trisomic pregnancies are associated
with altered maternal serum
concentrations of feto-placental
products
Detection rate of T 21 is 90% for a
false positive rate of 3% when used
in combination with Maternal
age,NT,FHR, Free B-HCG and PAPP-A

NEW ULTRASOUND MARKERS
Nasal bone
Facial angle
Ductus
venosus flow
Tricuspid
flow

NASAL BONE
= SIGN BETWEEN
TIP OF THE NOSE
AND FRONTAL
BONE

Present and Absent NB

NASAL BONE
Acts as an independent variable
Presence of NB reduces the aneuploidy risk ~3x
Absent NB after 12 wks,CRL 65 mm,increases the
risk of aneuploidy
Occurs in 67-73% of T21,,LR 48x
Occur in 1.5% of Euploid population

NASAL BONE LENGTH
It should be more than 2.5
mm @1st Trimester
More than 2.8mm at 15
wks(mean 4.7mm)
More than 5.6mm at 22
wks(mean 8.2mm)

FACIAL
ANGLE
• Measured between a line along the upper
surface of palate and a line which traverses
the upper corner of anterior aspect of
maxilla extending to the external surface of
the forehead.
• This is represented by the frontal bones or
an echogenic line under the skin below the
metopic suture that is usually open at this
gestational age

FACIAL
ANGLE

FACIAL ANGLE BET CRL 45-84MM
In Euploid fetuses mean facial angle decreases from
84deg to 76deg
FACIAL ANGLE IS ABOVE 95TH CENTILE
In 5% of Euploid fetuses
In 45% of fetuses with T21

DUCTUS VENOSUS FLOW
Fetus should not be moving
Magnification of the image should be such
that Fetal thorax and abdomen occupy
whole screen
Right ventral midsagittal view should be
obtained
Color flow mapping placed to view Umbi
vein,Ductus venosus and heart
Sample gate 0.5-1mm to avoid
contamination from adjacent veins and it
should be placed on yellowish alliasing
area

Criteria for DV
Angle of Insonation should be less than
30 degree
Filter should be set at 50-70Hz to allow
visualization of whole waveform
Sweep speed should be 2-3 cm/sec so
that waveforms are widely spread for
better assessment of a wave

DV

NORMAL

REVERSED a
WAVE
Is found in about 4% of normal
fetuses
It is associated with increased risk
for chromosomal abnormalities
Cardiac defects
Fetal death
However, in about 80% of cases
with reverse a wave the pregnancy
outcome is normal

TRICUSPID
FLOW
Magnification of the image should
be such that fetal thorax occupies
the whole screen
Apical 4 chamber view of the
heart should be obtained
Sample gate 2 -3mm and
positioned across the Tricuspid
valve
Angle of Insonation less than 30
degrees with IVS

CRITERIA FOR TRICUSPID FLOW
Sweep speed should be 2-
3mm/sec so that the wave forms
are widely spread
Sample volume should be placed
across the valve at least 3 times
in an attempt to interrogate the
complete valve

TRICUSPID

TRICUSPID REGURGITATION
Euploid fetuses: 1%
T21 fetuses: 55%
T18 fetuses: 30%
T13 fetuses: 30%

TRICUSPID REGURGITATION

IT a new ACRONYM FOR 2011
Intracranial translucency
or 4th ventricle
Bordered by 2 echogenic
lines, between brainstem
and choroid plexus

IT

Why IT ?
Normal fetus IT is always visible
measuring 1.5-2.5mm,parallel to NT
slightly parasagittal
Concept-Most open SB associated
with ACM
Leakage of CSF into amniotic cavity
result in hypotension in subarachnoid
space leads to caudal displacement of
brain and obliteration of cisterna
megna 4th ventricle with resultant
loss of IT

NORMAL AND ABNORMAL IT

ABNORMAL IT AND SB
IMAGE

NORMAL IT

ANATOMIC EVALUATION
Three major diagnostic groups
Always detectable
Potentially detectable
Undetectable

ALWAYS DETECTABLE GROUP
Anencephaly
Alobar holoprocencephaly
Omphelocele
Gastroschisis
Bodystalk anomaly
megacystis

POTENTIALLY DETECTABLE GROUP
Cardiac anomalies
Skeletal dysplasias
Limb amputations
Open NTDs
Renal agenesis
Facial clefts and
Diaphragmatic hernias

UNDETECTABLE GROUP
Microcephaly
ACC
Ventriculomegaly
Fetal tumours
Hydronephrosis
Echogenic lung lesions
Duodenal/Small bowel atresias

EXENCEPHALY ANENCEPHALY SEQUENCE
Exencephaly: Defined by
Acrania/No calvarium
Exposed brain degenerates over
time due to injurious environment
Anencephaly-Brain degenerates
over time
It is commonest NTD 1/1000 ,Rec
risk of 1.9%
Maternal Serum AFP is raised
Folic acid is preventive in 70%

ACRANIA

ALOBAR HOLOPROSENCEPHALY
1/1300 Prevalence
2/3rd are Aneuploidy(T18,T13)
and 1/3rd Euploidy
10% Recurrence risk if
Aneuploidy
1% Recurrence risk if Euploidy
Check for associated genetic
conditions Pallister hall,Smith-
Lemli-Optiz,

CHARACTERISTIC FEATURES
Monoventricle,Absent midline
structures, Fused Thalami
Additional features: Dorsal
sac,Displaced pan cake cortical tissue
Common facial
features:Hypotelorism, Single
orbit,Proboscis,Clefts
This should diagnosed after 10 wks
because no midline structures
developed

HOLOPROSENCEPHALY

Fused Thalami,Monoventricle

PHYSIOLOGIC
HERNIATION/OMPHELOCELE
NORMAL
<7 mm any age
<10mm <10 wks
Gone by 12 wks
Never contain liver

OMPHELOCELE
> 7mm <10 wks
> 10mm >10 wks
Persists beyond 12wks
Homogenous and rounder
May contain Liver

OMPHELOCELE
If only small bowel is included,association
with T18 more likely
70-90% have associated anomalies(50%
Cardiac)
Only 17% survive till Surgery due to TOP,
IUFD,Early NND
70% have increased AFP levels.

EXOMPHALOS

OMPHELOCELE

GASTROSCHISIS
It is a defect of abdominal wall by
definition
Herniation free floating loops of
bowel
Not covered by membrane
Clinically, Increased incidence <25
age,substance abuse
0-3% risk of
aneuploidy(karyotyping not
recommended)
5% associated structural anomalies

Absence of covering membrane

MEGACYSTIS
Normal bladder
We should able to visualize by 9-
10 wks
Between 2 umbilical arteries
>7mm in vertical diameter 1/3rd
Aneuploidy,T13 and T18
>15mm, all progressive
obstructive uropathy

7 to 15 mm
90% will resolve if Euploid
Can be because of Transient functional
neurogenic bladder
Delay in smooth muscle autonomic
innervation
Rescan after 2 wks and consider
karyotyping

MEGACYSTIS

UMBILICAL ARTERIES

POSTERIOR URETHRAL VALVES AND EUPLOIDY
Good prognosis based on fetal urine
electrolytes
Na<100meq/L,Cl<90meq/L,Osmolarity<21
0mOsm/L
No US evidence of dysplasia
Survival rate 81% vs.12.5% poor prognosis
Shunting no longer recommended
Mortality 43% with dismal long terms fetal
outcomes
Consider only in case of severe
oligohydramnios with normal appearing
kidneys and good electrolytes

KEY HOLE SIGN
Highly sensitive but no longer
considered specific for PUV
XY=PUV,,XX=Urethral atresia
1/3rd Boys with VUR may display
transient key hole sign
Bladder dysnergy
Look for thick walled and dilated
bladder
DDX:Consider VUR, Megacystic-
Microcolon-Hypoperistalsis,other
BOO,Prune belly

Key hole

FETAL ECHOCARDIOGRAPHY
If lie is
favourable,detection of
Cardiac defects increases
Advantage of detecting
lethal cardiac anomaly
early

Hypoplastic
left heart

TOF

AVSD

CONCLUSIONS
Screen and diagnosis are rapidly shifting
to first trimester
We have an ability to see more earlier
Better understanding of embryology
We still recommend follow up exam at
18-20 wks
Enormous differences in results
between different groups
Increase knowledge and standardization

First trimester scan

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