Prenatal diagnosis and screening is the testing for diseases or conditions in a fetus or embryo before it is before.

• It aims to detect birth defects e.g. neural tube defects, Down syndrome, chromosome abnormalities genetic disorders and other conditions, e.g. spina bifida, cleft palate, Tay Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile X syndrome
• Screening can also be used for prenatal sex discernment
• Sometimes, the tests are administered to determine if the fetus will be aborted, though doctors and patients also find it useful to Dx high-risk pregnancies early so that delivery can be scheduled in a tertiary care hospital where the baby can receive appropriate care

• Non-invasive (NIPT), including:
  • Before implantation:
    • Preimplantation genetic diagnosis, where during IVF procedures, cells are sampled from human emryos before implantation. It is in itself non-invasive, but IVF usually involves invasive procedures e.g. transvaginal oocyte retrieval
  • Trimester 1:
    • Fetal cells in maternal blood (FCMB), which is based on enrichment of fetal cells which circulate in maternal blood. Since fetal cells hold all the genetic information of the developing fetus, they can be used to perform prenatal Dx
    • Cell-free fetal DNA in maternal blood, which is based on DNA of fetal origin circulating in the maternal blood. Testing can potentially identify fetal aneuploidy, and gender of a fetus as early as 6 weeks into a pregnancy. Fetal DNA ranges from about 2-10% of total DNA in materna blood. It also allows whole genome sequencing of the fetus, thus determining the complete DNA sequence of every gene
  • Trimester 1 or 2:
    • Ultrasound detection (aka dating scans, booking scans), which is done from 7 weeks to confirm pregnancy dates, and look for twins
      • The specialized nuchal scan at 11-13 weeks may be used to identify higher risks of Downs syndrome
      • Later morphology scans from 18 weeks may check for any abnormal development
    • Fetal heartbeat, which is listening to the fetal heartbeat
  • Trimester 3:
    • Non-stress test, using a CTG during trimester 3, to monitor fetal wellbeing
• Less invasive:
  • Trimester 1:
    • Transcervical retrieval of trophoblast cells, involving cervical mucus aspiration, cervical swabbing, and cervical or intrauterine lavage, can be used to retrieve trophoblast cells for Dx purposes, including prenatal genetic analysis. Success rates range from 40-90%. It can be used for fetal sex determination and identify aneuploidies
  • Trimester 1 or 2:
    • Maternal serum screening, including;
      • Beta-hCG
      • PAPP-A
      • Alpha fetoprotein
      • Inhibin-A
• More invasive:
  • After 10 weeks:
    • Chorionic villus sampling (see page)
  • After 15 weeks:
    • Amniocentesis (see page)
  • At 24-34 weeks:
    • Percutaneous umbilical cord blood sampling, a Dx genetic test that examines blood from the fetal umbilical cord to detect fetal abnormalities

• Early morphology