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Prenatal Tests

Throughout your pregnancy you may be offered a variety of tests and procedures.

Prenatal Tests that are Routinely Offered:

Prenatal Genetic Screening

  • Indicates your CHANCE of having a baby with Down syndrome, trisomy 18 or open neural tube defects (e.g. spina bifida).
  • Screening is a personal choice. The information can provide reassurance, give you time to prepare for a child with special needs or set in motion plans to put the baby up for adoption or have an abortion. It can also create unnecessary worry or risks if you have decided to “take what comes.”
  • Your health care provider and/or genetic counsellor can help you with the decision to have prenatal screening by discussing the risks and benefits and your preferences.
  • Screening can start at 10 weeks. The tests offered depend on how far along you are.
    Screening usually involves one or more blood tests and an ultrasound done on the space at the back of baby’s neck (nuchal translucency scan).
  • You may be offered other tests that can diagnose if baby has one of these conditions. This may be another ultrasound, chorionic villus sampling (CVS), amniocentesis (amnio) or non-invasive prenatal testing (NIPT).
  • Speak to your health care provider about a prenatal appointment in the Genetics Program at Peterborough Regional Health Centre. You can meet with a nurse and a genetic counsellor to discuss your prenatal screening options, a positive screen or a genetic condition in your family history.


After 7 weeks
A scan that uses sound waves to help: confirm a pregnancy; estimate the due date, baby’s size, and the position of the placenta; and detect or rule out complications.

Glucose Screening (Glucose Challenge Test)

26-28 weeks
A blood test for high levels of sugar in the blood. It may indicate gestational diabetes. If positive, a special second test called the Glucose Tolerance Test, may be needed.

Group B Streptococcus Screening (GBS)

35-37 weeks
A swab to test for GBS bacteria; a common bacteria found in the vagina or rectum. If positive you will be treated with antibiotics during labour.

Prenatal Tests or Procedures that may be Recommended

Chorionic Villus Sampling (CVS)

11-14 weeks
A needle or small catheter that removes a sample of the placenta to diagnose some genetic conditions.

Amniocentesis (Amnio)

16-20 weeks
A needle that removes a sample of amniotic fluid to diagnose some genetic conditions.

Glucose Tolerance Test

24-28 weeks
A blood sample that is taken once every hour for three hours after you drink a special sweetened drink. It is a more involved test than glucose screening.

Rh Immune Globulin

28-32 weeks and soon after your baby’s birth (if your baby’s blood is RH+)
An injection that is given if you are Rh- to prevent your blood from reacting to your baby’s blood in case it is Rh+. Rh immune globulin is also given after major bleeding in pregnancy and after delivery if your baby is Rh+. It prevents problems in a future pregnancy. After delivery, if your baby is Rh+, you will be given a second injection.

Non-Stress Test

After 25-28 weeks
Two belts wrap around your belly to measure contractions and baby’s heart rate as he moves. It may be done with a Biophysical Profile.

Biophysical Profile

After 32 weeks
Combines fetal heart rate monitoring and an ultrasound that checks on baby’s body movements, muscle tone, and the amount of amniotic fluid.

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