Obstetric Ultrasound and Non-invasive Prenatal Testing

Dr. Chang has headed the Fetal Assessment Unit (Centre for Prenatal Diagnosis and Obstetric Ultrasound) at Thomson Medical Centre since 1998. He performs obstetric ultrasound scans, amniocentesis and chorionic villus sampling procedures in the Unit. He is also accredited by the Fetal Medicine Foundation (London) to perform first trimester Nuchal Translucency ultrasound (accredited since 2000).

His special areas of interest are:
  • Non-invasive Prenatal Testing: Harmony Test (after 11 weeks of pregnancy)
  • First trimester NT ultrasound to screen for Downs Syndrome
  • Genetic ultrasound scan to assess risk of fetal chromosome abnormalities
  • Assessment of fetal structural anomalies, counselling and prognosis
  • Ultrasound assessment of high-risk and complicated pregnancies (twins, intra-uterine growth restriction)
  • Prenatal invasive procedures (amniocentesis, CVS and fetal blood sampling)
  • 4D ultrasound


Important Ultrasound Assessments in Pregnancy
  • First Trimester Combined Screening (also known as OSCAR) - Ultrasound Assessment of Nuchal Translucency and Nasal Bone, together with Biochemical Screening. This scan and blood test on Mum is performed between 11 weeks and 13 weeks 6 days of pregnancy. It can detect up to 92% of all pregnancies affected by Downs syndrome
  • Fetal Anomaly Ultrasound Scan - This scan screens for major fetal malformations, including abnormalities of the brain, face, heart, lungs, iFetal Anomaly Ultrasound Scan - This scan screens for major fetal malformations, including abnormalities of the brain, face, heart, lungs, intestinal system, kidneys, spine and limbs. It is performed between 18 and 21 weeks of pregnancy.
  • Growth and Doppler Ultrasound Scan (Uterine, Umbilical, Middle Cerebral, Ductus Venosus) to help detect early signs of oxygen deprivation in the growth restricted fetus, Pataus Syndrome).
  • Invasive fetal medicine diagnostic procedures to diagnose fetal chromosome abnormalities (Downs syndrome, Edwards syndrome, Pataus Syndrome).

Invasive procedures for fetal infections (rubella, cytomegalovirus, toxoplasmosis, parvovirus)

Invasive procedures for genetic syndromes (Thalassaemia, Tay-Sachs, cystic fibrosis, achondroplasia, Duchennes muscular dystrophy, Prader-Willi, Angelmans, di George syndromes)

Rapid testing for the three commonest fetal trisomies using PCR or FISH will yield results within 48 hours.

Best time to do the tests:

Amniocentesis: 15 - 16 weeks

Chorionic Villus Sampling: 11 - 12 weeks

Fetal blood sampling: 20 - 22 weeks

 
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