Dr. Chang heads the Fetal Assessment Unit (Centre for Prenatal Diagnosis and Obstetric
Ultrasound) at Thomson Medical Centre. He has performed more than 20,000 obstetric ultrasound
scans, 6000 amniocentesis and 800 chorionic villus sampling procedures over the last 14 years.
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:
- 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