Fetal ultrasound

Normal fetal cardiac situs

Heart apex and stomach should both lie on the fetal left side.

Normal fetal cardiac axis

Approximately 45 degrees towards the fetal left.

Normal fetal heart size

Occupies approximately one-third of the fetal thorax.

Four-chamber view (4CH)

Demonstrates both atria and ventricles with atrioventricular valves and interventricular septum.

Normal atrioventricular valve offset

Tricuspid valve inserts more apically than the mitral valve.

Moderator band

Muscular structure near the apex of the right ventricle used to distinguish RV from LV.

Foramen ovale

Allows blood to flow from the right atrium into the left atrium during fetal life.

Foramen ovale flap

Septum primum opens into the left atrium.

Pulmonary veins

At least one pulmonary vein should be demonstrated entering the left atrium during routine cardiac assessment.

Descending aorta on 4CH

Located posterior to the left atrium and anterior to the spine.

Normal ventricular sizes

Right and left ventricles should be relatively balanced during mid-gestation.

Left ventricular outflow tract (LVOT)

Demonstrates continuity of the interventricular septum with the anterior aortic wall.

Right ventricular outflow tract (RVOT)

Demonstrates the pulmonary artery arising from the right ventricle and crossing the aorta.

Normal great artery relationship

Aorta and pulmonary artery cross rather than run parallel.

Three-vessel view (3VV)

Demonstrates pulmonary artery then aorta then superior vena cava from fetal left to right.

Normal 3VV vessel sizes

Pulmonary artery is largest followed by aorta then superior vena cava.

Three-vessel-trachea view (3VT)

Demonstrates aortic and ductal arches in relation to the trachea.

Normal 3VT appearance

Aortic arch and ductal arch form a left-sided V configuration with flow towards the descending aorta.

Normal aortic arch

Gives rise to the brachiocephalic trunk and left common carotid and left subclavian arteries.

Normal ductal arch

Connects the pulmonary artery to the descending aorta without head and neck branches.

Aortic arch versus ductal arch

Aortic arch has head and neck branches whereas ductal arch does not.

Normal fetal ductus arteriosus

Connects pulmonary artery to descending aorta and bypasses the lungs.

Normal fetal ductus venosus

Shunts oxygenated umbilical venous blood towards the inferior vena cava.

Normal fetal umbilical vein

Carries oxygenated blood from the placenta towards the fetus.

Normal fetal umbilical arteries

Carry deoxygenated blood from the fetus towards the placenta.

Ventricular septal defect (VSD)

Opening in the interventricular septum; may be muscular or perimembranous.

Atrioventricular septal defect (AVSD)

Abnormal atrioventricular junction with a common AV valve and defects involving the atrial and ventricular septa.

AVSD and aneuploidy

Strong association with trisomy 21.

Tetralogy of Fallot (TOF)

VSD plus overriding aorta plus pulmonary stenosis or RVOT obstruction plus right ventricular hypertrophy.

TOF key ultrasound finding

Overriding aorta with malalignment VSD and narrowed pulmonary outflow tract.

TOF on 3VV

Pulmonary artery may be smaller than the aorta due to RVOT obstruction.

Transposition of great arteries (d-TGA)

Aorta arises from RV and pulmonary artery arises from LV.

TGA key ultrasound finding

Great arteries run parallel rather than crossing.

TGA four-chamber view

May appear normal because ventricular and atrial anatomy can be preserved.

TGA on 3VV

Abnormal vessel arrangement with possible apparent two-vessel appearance.

Double outlet right ventricle (DORV)

Both great arteries arise predominantly from the right ventricle and a VSD is usually present.

DORV versus TGA

DORV has both great arteries predominantly connected to RV whereas TGA has ventriculoarterial discordance.

Truncus arteriosus

Single arterial trunk supplies systemic and pulmonary circulations with an associated VSD.

Truncus arteriosus key ultrasound finding

Single large arterial trunk overriding a VSD with pulmonary arteries arising from the trunk.

Truncus versus TOF

Truncus has one common arterial trunk whereas TOF has separate aorta and pulmonary artery.

Hypoplastic left heart syndrome (HLHS)

Underdevelopment of LV and often mitral valve and aortic valve and ascending aorta.

HLHS four-chamber view

Small or poorly developed LV with right ventricular dominance.

HLHS on 3VT

Small aortic arch compared with ductal arch; retrograde aortic arch flow may be present.

HLHS ductus arteriosus

Often large and essential for systemic circulation.

Coarctation of aorta (CoA)

Narrowing of the aortic arch usually near the aortic isthmus.

CoA four-chamber view

May show RV dominance or appear relatively normal.

CoA on 3VT

Aortic arch may be disproportionately small compared with ductal arch.

CoA key limitation

Prenatal diagnosis is difficult because ductal flow can mask arch obstruction.

Pulmonary stenosis

Narrowed pulmonary valve or outflow tract with possible post-stenotic dilatation.

Pulmonary atresia

No patent connection through the pulmonary valve; pulmonary blood flow may depend on the ductus arteriosus.

Pulmonary atresia on 3VT

Small or absent antegrade pulmonary outflow with possible reversed ductal flow.

Ebstein anomaly

Apical displacement of tricuspid valve with atrialisation of part of RV.

Ebstein anomaly ultrasound findings

Enlarged right atrium with abnormal tricuspid valve insertion and tricuspid regurgitation.

Right aortic arch (RAA)

Aortic arch courses to the right of the trachea rather than the left.

Right aortic arch with left ductus

May produce a U-shaped configuration around the trachea and raise suspicion of a vascular ring.

Vascular ring

Vascular structures encircle the trachea and oesophagus with potential postnatal compression.

Double aortic arch

Two aortic arches surround the trachea and form a complete vascular ring.

Aberrant right subclavian artery (ARSA)

Right subclavian artery arises as the last branch of a left aortic arch and usually passes behind the oesophagus.

ARSA and aneuploidy

Can be a soft marker for trisomy 21.

Persistent left superior vena cava

Additional venous vessel seen left of pulmonary artery on 3VV and commonly drains into coronary sinus.

Persistent LSVC ultrasound clue

Additional vessel on left of pulmonary artery with possible dilated coronary sinus.

Total anomalous pulmonary venous connection (TAPVC)

Pulmonary veins drain into systemic venous circulation rather than directly into LA.

TAPVC ultrasound clue

Failure to demonstrate normal pulmonary venous entry into LA with possible abnormal venous confluence.

Cardiomegaly

Enlarged fetal heart occupying an abnormally large proportion of thorax.

Fetal pericardial effusion

Fluid surrounding the fetal heart; significant collections require assessment for hydrops and cardiac dysfunction.

Fetal arrhythmia

Abnormal fetal cardiac rhythm assessed using M-mode or spectral Doppler.

Fetal bradycardia

Sustained fetal heart rate below 110 bpm.

Fetal tachycardia

Sustained fetal heart rate above 160 bpm; persistent marked tachycardia warrants rhythm assessment.

Small for gestational age (SGA)

Estimated fetal weight below the 10th percentile without necessarily having pathological growth restriction.

Fetal growth restriction (FGR)

Fetus has failed to achieve its growth potential; abnormal growth and Doppler findings may support placental insufficiency.

Symmetrical FGR

Head and abdominal measurements are proportionately reduced; may occur with early insults or genetic abnormalities.

Asymmetrical FGR

Abdominal circumference is disproportionately small relative to head measurements; often associated with placental insufficiency.

Small abdominal circumference in FGR

Reduced hepatic growth and fat deposition due to limited nutrient and oxygen supply.

Umbilical artery PI above 95th percentile

Suggests increased placental vascular resistance.

Absent end-diastolic flow (AEDF)

No forward umbilical arterial flow during diastole due to markedly increased placental resistance.

Reversed end-diastolic flow (REDF)

Umbilical arterial blood flows backwards during diastole; severe placental vascular dysfunction.

Middle cerebral artery brain-sparing

Reduced MCA PI due to cerebral vasodilatation in response to fetal hypoxaemia.

Cerebroplacental ratio (CPR)

MCA PI divided by UA PI; low ratio suggests redistribution or placental dysfunction.

Ductus venosus absent or reversed a-wave

Abnormal venous Doppler associated with impaired fetal cardiovascular function and increased risk of adverse outcome.

Early-onset FGR

Growth restriction diagnosed before 32 weeks; more commonly associated with severe placental disease.

Late-onset FGR

Growth restriction diagnosed at or after 32 weeks; UA Doppler may remain normal.

Oligohydramnios

Reduced amniotic fluid volume; causes include placental insufficiency and membrane rupture and renal abnormalities.

Polyhydramnios

Increased amniotic fluid volume; causes include maternal diabetes and impaired fetal swallowing and gastrointestinal obstruction.

Amniotic fluid index (AFI) oligohydramnios

AFI of 5 cm or less.

Deepest vertical pocket oligohydramnios

Single deepest pocket less than 2 cm.

Deepest vertical pocket polyhydramnios

Single deepest pocket at least 8 cm.

AFI polyhydramnios

AFI at least 24 cm.

Placenta previa

Placenta covers the internal cervical os.

Low-lying placenta

Placental edge lies less than 20 mm from internal cervical os without covering it.

Placental abruption

Premature placental separation; ultrasound may show haematoma but a normal scan does not exclude abruption.

Vasa previa

Unprotected fetal vessels course over or near the internal cervical os; colour Doppler and transvaginal assessment are important.

Velamentous cord insertion

Umbilical vessels travel through membranes without Wharton's jelly before entering placenta.

Marginal cord insertion

Umbilical cord inserts at or near the placental edge.

Single umbilical artery

Umbilical cord contains one artery and one vein rather than two arteries and one vein.

Single umbilical artery associations

Increased association with structural abnormalities particularly cardiac and renal anomalies.

Twin-to-twin transfusion syndrome (TTTS)

Monochorionic twins develop discordant amniotic fluid volumes due to placental vascular anastomoses.

TTTS donor twin

Typically has oligohydramnios and a small or non-visible bladder.

TTTS recipient twin

Typically has polyhydramnios and a distended bladder with risk of cardiac overload.

Twin anaemia polycythaemia sequence (TAPS)

Monochorionic twins have discordant MCA peak systolic velocities due to chronic blood transfusion.

Fetal anaemia Doppler

MCA peak systolic velocity above 1.5 MoM suggests moderate to severe fetal anaemia.