Prenatal Genetic Screening and Testing
The goal of prenatal genetic screening is to identify pregnancies at higher risk for chromosomal abnormalities, in which case diagnostic testing can be offered for confirmation. The available options for prenatal genetic screening are complex and ever-changing. Perinatal Services BC provides a useful decision-making tool regarding the pros and cons of screening and the available options. The most recent update was published in April 2019.
Screening is very time-sensitive, with certain tests needing to be arranged at the end of the first trimester, and others in the second trimester. In cases where the first OB appointment is booked after the first trimester, these tests may need to be initiated by the referring provider.
MSP-funded options for screening depend on a woman’s age and other characteristics. What follows is a simple guide for women with spontaneously-conceived singleton pregnancies.
Women in special circumstances (multiples, IVF +/- ICSI, +/- PGT-A, personal or family history of chromosomal anomalies) will need to consult their OB for options that pertain to their specific circumstances. In complex situations, referral to Medical Genetics will be required.
SIPS (Serum INtegrated Prenatal screenING)
This is the MSP-funded option for women under 35 at delivery. It includes 2 sets of hormonal blood tests done in the first trimester (SIPS-1: 9w0d-13w6d; ideal 10w0d-11w6d) and the second trimester (SIPS-2: 14w0d-20w6d; ideal 15w0d-16w0d).
Results are reported 1-2 weeks after completion of SIPS-2.
If the risk of Down syndrome is greater than 1:900, NIPT is offered free of charge. If the risk is greater than 1:300, women can choose NIPT or amniocentesis.
IPS (Integrated prenatal screenING)
This test is available to women age 35 or older at delivery. It consists of the SIPS blood tests PLUS a specialized ultrasound done at 11w0d-13w6d (ideal 12w0d-13w3d) to measure the nuchal translucency (NT).
It is considered positive if the risk of Down syndrome is higher than 1:200, in which case further testing with either NIPT or amniocentesis is offered.
Quad Screen
This is essentially the SIPS-2 blood test and is the only MSP-funded option for women who have missed the window for SIPS-1 and/or the NT ultrasound.
If the risk of Down syndrome is greater than 1:900, NIPT is offered free of charge. If the risk is greater than 1:300, women can choose NIPT or amniocentesis.
NIPT (non-invasive prenatal testing)
NIPT is a blood test that screens for chromosomal abnormalities (trisomy 21, 18, 13, sex chromosome abnormalities) by measuring fetal DNA in the maternal circulation. It is generally more accurate than the hormonal-based SIPS and IPS.
It can be done as early as 9-10 weeks of pregnancy. The sex of the baby can be included in the report, upon request.
Currently, it is available on a private-pay basis at a cost of $495-650. Different ‘brands’ exist, with similar accuracy, but differences in methodology. The Panorama test is available through Lifelabs. Additional screening for rare disorders caused by chromosomal micro-deletions is available for about $250. The Harmony test is available through Dynacare nurse home collection, the hospital labs, and certain fertility clinics. Perinatal Services BC provides a useful summary.
Women with a positive SIPS/Quad (1:900 risk) or IPS (1:200 risk) are eligible for MSP-funded NIPT (Harmony only). The OB will complete a special form for this.
CVS and Amniocentesis
Women over 40 and women with a positive screening test (SIPS/Quad 1:300 risk or IPS 1:200 risk) are eligible for invasive prenatal testing. These tests are highly accurate but carry a risk of pregnancy loss.
Chorionic Villus Sampling (CVS) is done at 10.5-13 weeks, and it involves taking a sample of the tissue that will eventually form into the placenta. Results are available sooner than with amnio, but the risk of pregnancy loss is higher at 1-2%.
Amniocentesis is done after 15.5 weeks and involves taking a sample of the amniotic fluid. The risk of pregnancy loss is about 0.5% or 1 in 200.