Screening tests for antenatal diagnosis

Maternal blood for....

• blood group + Rh antibodies
• Hep B
• Syphilis
• Rubella
• HIV (after counselling and maternal consent)
• neural tube defects
• Down's syndrome

Ultrasound screening for ....

• gestational age - if performed before 20/52
• multiple pregnancies
• structural abnormalities
• fetal growth monitoring - abdo + head circumference and femur length
• amniotic fluid volume
  - oligohydramnios (reduced fetal urine production - dysplastic /absent kidneys or obstructive uropathy, prolonged rupture of membranes -> IUGR) --> Pulmonary hypoplasia and limb + facial deformities from pressure on fetus (Potter's Sx)
  - polyhydramnios (assoc. with maternal diabetes & fetal G.I. atresia)

Techniques for antenatal diagnosis

• Detailed Ultrasound - structural malformations
• Amniocentesis - chromosomal analysis, Alphafetoprotein+acetylcholinesterase (NTD), bilirubin estimation (rhesus disease), enzyme analysis (inborn errorof metabolism)
• Transabdominal chorionic villus sample - chromosomal analysis, enzyme analysis (inborn error of metabolism), DNA analysis (thalassaemia, haemophilia A+B, CF, Duchenne's)
• Fetal blood sample - rapid chromosomal anaylsis (fetal malformations or severe IUGR), assessment of severe rhesus & platelet isoimmunisation, congenital infectoin serology
• Fetal tissue sampling - skin biopsy (severe congenital skin disorders)