Prenatal Screening
Prenatal Screening is offered for all people in early pregnancy, to test for Trisomy 21, 18, and 13.
Enhanced first trimester screening (Efts) is offered for people between gestational ages of 11 weeks, 2 days to 13 weeks, 3 days. Efts is a screening tool that tells you the chance of having a baby with trisomy 21 (Down Syndrome) or Trisomy 18 (Edwards Syndrome). This chance increases with maternal age. Efts is paid for by OHIP. Enhanced first trimester screening includes having an ultrasound to determine the Nuchal Translucency (NT) (which is the thickness of the back of the fetal neck), followed by a blood test, that looks at specific markers in the blood: Pregnancy-associated plasma protein A (PAPP-A), human chorionic gonadotropin (HCG), Alpha-fetoprotein (AFP), and Placental growth factor (PIGF).
Maternal serum screening (MSS) is a genetic test that your health-care provider can arrange in the second trimester of pregnancy. It is a reliable test if you are too late for the Efts. This test uses a combination of maternal age and blood work to give you the relative chance that the baby has trisomy 21 (Down syndrome) or trisomy 18. MSS can be done between 14 weeks and 20 weeks 6 days gestation. It measures human chorionic gonadotropin (HCG), alpha-fetoprotein (AFP), inhibin-A, and unconjugated estriol (UE3).
Non-invasive Prenatal Testing (NIPT) is a blood test available from 9 or 10 weeks, that may be done if you have a positive Efts. It is also offered for people expecting twins. Clients may request to have NIPT, however, unless they have certain risk factors or a positive efts, they must pay for it.
During pregnancy, there are small pieces of genetic material (known as DNA) from the placenta that can be found in the bloodstream. The placenta and the baby usually have the same genetic make up.
Non-invasive prenatal testing (NIPT) looks at placental DNA and can tell if there is a high or a low chance for each of the chromosome differences that are screened. It is important to remember that NIPT is a screening test and will not give a definite answer about any of the chromosome differences. NIPT screens for Trisomy 21, 18, and 13. False positives with NIPT are very low. NIPT can more accurately tell you the chance to have a baby with trisomy 21 and trisomy 18 in the pregnancy, compared to other forms of prenatal screening (like Efts or MSS)