Antenatal Diagnosis

Question 1

What are some pregnancy ultrasounds you can get?

Answer 1

• Morphology Scan - 20-22 weeks
• 1st trimester US/12 week scan (dating/risk scan) - 11-13weeks
• Growth scan
  
  • MCA - PSV (peak systolic velocity) - pulsatility index. Look for anaemia.
  • amniotic fluid >20, <5.

Question 2

What are the things you look at when assessing risk in the 1st Trimester Scan?

Answer 2

• Background Risk:
  
  • age
  • previous T21 baby/chromosomal abnormality?
  • gestation
• nuchal translucency (>2.5mm)
  
  • risk of cardiac, lymphatic, neuromuscular abnormalities
  • image: gestation 11+1 - 13+6, mid-sagital view, CRL 45-84mm
• nasal hypoplasia (ossified is protective)
• Serum βhCG - higher in T21
• PAPP-A - lower in T21
• Others:
  
  • ductus venosus flow (hard to standardise, good for confirmation) association with T21 and cardiac
  • crown-rump length
  • visualise brain

Followup:

• gives a MOM - multiples of the median. ONLY RISK.
• 1st trimester screening is important because 50% will look normal by Trimester 2.

Structural abnormalities:

• anencephaly
• gastroschisis
• absent hand/foot
• exomphalos
• renal rarely detectable.
• Diaphragmatic hernia in 50%

Question 3

What is cfDNA and NIPT? How can it be used in Antenatal screening?

Answer 3

cfDNA = cell-free DNA

• can be measured in maternal plasma through MPS (massive parallel sequencing)
• overabundance of cfDNA from fetus. Need 4% fetal fraction.
• T13, 18, 21, X and Y.
• available from 9 weeks gestation and takes 2 weeks.
• not diagnostic
• 10 week test for 12 week scan.

Question 4

What is involved in the 19-22week scan?

Answer 4

• Mothers cervix (pre-term labour)
• T21 a few markers:
  
  • aberrant subclavian artery
  • hydronephrosis
  • short femur
  • hyperechogenic bowel
• congenital anomalies:
  
  • congenital heart disease - conotruncal anomalies
    
    • still hard - false +/-
  • diaphragmatic hernia
    
    • lung to head ratio
  • ventriculomegaly (10mm-15mm mild, >15mm severe
  • fetal callosal anomalies (agenesis or disordered, ACC or DCC)

Question 5

What are some Obstetric indications for an MRI?

Answer 5

• fetal abnormality assessment
  
  • after 20 weeks
  • fetal surgical workup
• high risk pregnancies for cerebral ischaemia (TTTS in multiple pregnancies)
• placenta accreta or suspected percreta
• maternal illness
• postmortem

Brain MRI -

• suspected abnormality on US
  
  • e.g. FETO (fetal endoscopic trachael occlusion)
  • fetal tumours
• high risk fetus: TTTS, severe anaemia, genetic indication

Question 6

What is the Quadruple blood test done between weeks 14 and 20+6? What does it measure?

Answer 6

1. Free β-hCG
2. 𝜶-fetoprotein
3. unconjugated oestriol
4. Inhibin A

Question 7

What third trimester screening is generally performed?

Answer 7

• US:
  
  • not as effective in 3rd trimester
  • fetal circulation, size, placental site monitored previously
• Doppler:
  
  • MCA
  • umbilical artery
  • ductus venosus

Question 8

What are some diagnostic tests for Down’s Syndrome? What is involved and when do you do them?

Answer 8

CVS

• 10-12weeks
• 1-2% miscarriage rate
• sampling of placental tissue
• TOP by curettage
• preferred for DNA

Amniocentesis

• 15-20weeks
• 0.5-1% miscarriage
• sampling of fetal tissue
• TOP by induction