Invasive diagnostic testing for chromosomal analysis can be done by chorionic villi sampling (CVS) or amniocentesis.
For more details about the two procedures, See Appendix 3 of the prenatal screening Guideline.
- Trisomy 21 (Down Syndrome) Positive SIPS or Quad with a risk greater than 1/300.
- Trisomy 21 Positive IPS with a risk greater than 1/200.
- Trisomy 18 Positive SIPS/IPS/Quad with a risk greater than 1/300.
- Positive NIPT screen.
- Maternal age of 40 + at EDD with singleton pregnancy OR 35 + at EDD for twin or higher multiple pregnancies.
- Patient is too late for Quad screen and maternal age 35+ at EDD.
- Previous pregnancy / child with trisomies 13, 18 or 21 or sex chromosomal aneuploidy excluding Turner syndrome.
- Pregnancy conceived by IVF and ICSI
- Previous pregnancy / child with a chromosomal structural abnormality including copy number variant.
- Pregnant person or father of pregnancy is a carrier of a chromosomal abnormality that increases the risk of an unbalanced chromosomal complement in their offspring.
- Pregnancy conceived from the transfer of a mosaic embryo.
- Ultrasound finding(s) that increases the risk of a fetal chromosomal abnormality.
- Atypical findings on NIPT
For Indications 1-8, health care providers can arrange the procedure directly. Amniocentesis is offered at BC Women's hospital, Surrey Jim Pattison, and Victoria General hospital. CVS is offered at BC Women's hospital only. Referrals can be made based on the location best suiting the patient's place of residence.
For indications 9-13, the patient should be referred to Medical Genetics in Vancouver or Victoria.
The type of chromosomal analysis that will be carried out on the sample taken at the time of the CVS/amniocentesis will depend on the indication for testing and the site where the procedure is done. Details are provided in the table below.