II. Definition
- Definitive, first trimester Antenatal Screening for fetal chromosomal abnormalities
III. Indications
- Antenatal Screening for fetal chromosomal abnormalities for high risk pregnancies
IV. Protocol
- Performed between 10-13 weeks gestation
- Placental tissue sampling techniques
- Transabdominal sampling
- Transcervical sampling
- Higher Incidence of pregnancy loss than with abdominal sampling
- Indicated if placenta posterior or bowel blocks abdominal sampling
V. Adverse Effects
- Pregnancy loss
- Risk: 0.6 to 4.6% (higher rate than with Amniocentesis)
- Limb reduction defects
- Gestational age 10-13 weeks: Risk does not exceed general population risk (6 per 10,000)
- Gestational age <10 weeks: 1-2% risk of limb reduction defect
VI. Efficacy: Down Syndrome detection
- Test Sensitivity: 97.8%
- Test Specificity: 98-99%