2nd trimester scan

2nd trimester scanning

2nd trimester scanning

Confirming dating of pregnancy

Fetal normality/ abnormality

Placental localisation

AF volume

BPD

Correct levels

2 views: lateral ventricle view, thalamic view

More accurate than CRL +/- 5 days

Maximum diameter of transverse section of fetal skull at level ofthe parietal eminences

BPD

Lateral ventricle view:

Rugby shaped skull

Long midline equidistant prox-distal skull echoes

Cavum septum pellucidum (CSP) bisecting midline

Two anterior horns of lat ventricle- symmetrical

Post horns of lat ventricle- symmetrical

BPDLateral ventricle view

BPD

Thalamic view:

Rugby ball shape

Short midline

CSP

The thalami (arrow head)

BPDThalamic view

BPD

Both levels comparable

HC/OFD same level

Outer to outer

Outer to inner

OA/OP position

BPDTo obtain the correct level

BPDEstimating GA from BPD:

Not to rely on estimates of GA from US software

GA should not be made from single parameter

Different charts

GA and growth require different charts and charting

BPDEstimating GA from BPD

BPDConfirming or assigning GA:

If LMP and earlier dating 1st trimester US matches- stick to this date

2nd trimester US is only for growth and not for dating

If the 2nd trimester US is the first scan done error is greater:

below 24w +/- 2 w

After24w >3w

Head circumference

Same view as BPD

Outer to outer

Superior to BPD for dating

Abdominal circumference

Landmark features:

Circular section with ribs

One vertebra -triangle of 3 white spots

Umbilical vein (short) - hockey stick

Stomach left abdomen

Good for dating of pregnancy

Sensitive to growth aberrations

Fetal weight assessment

Abdominal circumference

Femur length

As accurate as BPD for GA

From 12w to term

Slide probe caudally from AC section till iliac bones

Cross section of 1 femur seen

Upper femur for measurement

Rotate

Femur length


Placenta is more echogenic than myometrium

Alignment of probe standardised

Cervix to the right

Fundus to the left


Cervical canal directly posterior to bladder

Lower edge >5 cm from internal os

<5cm low lying

Placentae previa after 28w

Braxton hicks


Localisation at 20-22w

5% low lying

Only 1% placenta previa

Amniotic fluid volume

Produced by fetal kidneys (urine) and removed by fetal bowel (swallowing)

Oligohydromnios = decreased volume

Polyhydromnios = increased volume

Measurements : Visual

Max vertical depth 3cm

AFI - <5cm =oligo, >25cm = poly

Fetal anatomy assessment

Dependant on sonographer- correct images, correct interpretation

Go through all-complete coverage--> then no major abnormalities will be missed

E.g.After 12w - anencephaly


After 20-22w:

encephalocoele

cystic hygroma

abdominal wall defect

lemon sign - spina bifida

banana sign - hydrocephalus

severe limb reduction

ascites

pleural effusion

severe oligo/ polyhydramnios


Cerebral ventricles


Anterior horn


Posterior horn


AVHR/PVHR:

< 0.5 after 18w gestation

Ventriculomegaly


Fetal heart:

Occupy 1/3 with apex pointing to the left

3 views of the heart:

4 chamber view

2 outflow tract views


Fetal heart:

moderator band = right ventricle

2 ventricles/ walls of equal size

2 atria / walls of equal size

apex point left of fetal chest

foramen ovale moving in left atrium

pulmonary veins entering left atrium

motion of mitral valves (left side) regular

motion of tricuspid valves (right side) regular

'offset crux' of the heart: AV valve should not insert into IV septum at the same level

intervertebral septum should be complete


Fetal heart:

Abnormalities of 4c view:

No disparity in size between 2 ventricles

Tricuspid/ mitral valve defects:

Enlargement of atrium

Hypoplasia of ventricle


eg: (i) regurgitation of tricuspid valve - enlarged right atrium

(ii) hypoplastic left heart syndrome - left ventricle small

(iii) coarctation - right ventricle enlarged

(iv) Ebstein anomaly - enlarged right atrium due to abnormal implantation of tricuspid valve

normal IV septum - excludes VSD

normal offset crux - exclude AVSD

Both ASD & AVSD are assessed with trisomy 21


Fetal heart:

The aortic outflow tract rotate to right fetal shoulder


Demonstrate left ventricle: continuity of IV septum--> ant wall of aorta--> aortic valve & short section of ascending aorta

Abnormal AOT:

Overriding aorta

Aortic stenosis

Double outlet right ventricle

Fallot's tetralogy


Pulmonary artery outflow tract:

Demonstrate:

Right ventricle

Pulmonary valve

Main pulmonary artery abnormal in double outlet right ventricle & pulmonary stenosis


Fetal abdomen:

Single left sided stomach bubble--> after 16w

Cord insertion

Abdominal defects --> oomphalocoele, gastrochisis

Kidneys


Cleft lip and palate:

Incidence 1:700 births

80% isolated incidence

But association with trisomy 13 &18, anti epileptics drugs


Fetal sex:

Recognisable from 14 weeks

Craniospinal abnormality

Causes of increased AFP


Between 16-24w --> only as a marker


Hydrocephalus

Craniospinal abnormalityEncephalocoele

Craniospinal abnormalityHydrancephaly

Porencephalic cysts

Craniospinal abnormalityDandy walker

malformation

Chest abnormalityDiaphragmatic hernia

Fetal abdominal abnormality

Double bubble- duodenal atresia

Fetal abdominal abnormalityDouble bubble-

oesophageal atresia

Fetal abdominal abnormalityDilated bowels


Oomphalocoele

Fetal abdominal abnormalityGastrochisis


Renal agenesis

Cystic disease of the kidneys


Fetal hydrops

2nd trimester scan

Education

Transcript of 2nd trimester scan