Pregnancy comes with a lot of excitement — and often, a long list of tests. You may hear terms like “nuchal translucency” or “GBS swab” and wonder what they actually mean for you and your baby.
At Balancing Birth to Baby, we believe that knowledge = confidence. Here’s your trimester-by-trimester guide to the most common prenatal tests and screenings offered in Ontario — explained in plain language so you know what to expect, why it’s done, and how results may (or may not) affect your pregnancy.
First Trimester (up to 14 weeks)
Blood Tests (initial prenatal bloodwork)
What it is: A standard blood draw, usually at your first prenatal appointment.
Why it’s done:
- Blood type and Rh factor: Important because if you’re Rh-negative and your baby is Rh-positive, you may need an injection (Rh immune globulin) later in pregnancy to prevent complications in future pregnancies.
- Hemoglobin/iron levels: Checks for anemia, which can cause fatigue and may need treatment.
- Immunity checks: Confirms if you’re immune to rubella (German measles) and varicella (chickenpox). If not, your provider will note this for after birth, since live vaccines aren’t given during pregnancy.
- Infection screening: HIV, syphilis, hepatitis B (and sometimes hepatitis C). If positive, treatment or special care can help protect your baby.
What results might mean: Most results are reassuring. If something unusual shows up, your provider will explain the next steps, which might include medication, supplements, or follow-up testing.
Urine Test
What it is: A simple urine sample.
Why it’s done: Checks for urinary tract infections (which can be more common in pregnancy), kidney health, and sometimes sugar or protein in the urine.
What results might mean: If an infection is found, antibiotics safe for pregnancy may be prescribed. Protein or sugar in the urine could mean extra monitoring for conditions like pre-eclampsia or gestational diabetes later on.
Dating Ultrasound (8–12 weeks)
What it is: An early ultrasound using sound waves to see your baby.
Why it’s done:
- Confirms your due date more accurately than your last period.
- Checks if you’re having twins or more.
- Confirms heartbeat and growth.
What results might mean: Most families simply get reassurance and a first glimpse of their baby. Sometimes, if growth doesn’t match your dates, your due date may be adjusted or a follow-up scan suggested.
Prenatal Genetic Screening (11–14 weeks)
What it is: Options include a blood test + ultrasound (called First Trimester Screening) or a more advanced Non-Invasive Prenatal Test (NIPT).
Why it’s done: Screens for chromosomal differences (like Down syndrome, trisomy 18, trisomy 13).
- NT ultrasound: Measures fluid at the back of the baby’s neck, which can sometimes signal a higher risk.
- Blood test: Looks at hormone levels that can indicate certain conditions.
- NIPT: A blood test that analyzes fragments of the baby’s DNA in your blood. It’s more accurate than standard screening, but it is not always covered by OHIP.
Cost in Ontario: Unless you meet certain high-risk criteria (like being over age 40 or having an abnormal first screening), NIPT is self-paid. The cost usually ranges from $300–$500, depending on the lab and whether you add extra conditions to the panel.
What results might mean: These are screenings, not diagnoses. A higher-risk result doesn’t mean your baby has a condition — it simply means further diagnostic tests (like CVS or amniocentesis) may be offered.
Second Trimester (15–22 weeks)
Maternal Serum Screening (15–20 weeks)
What it is: A blood test sometimes called the “quad screen.”
Why it’s done: Screens for chromosomal differences and neural tube defects (like spina bifida).
What results might mean: If flagged as higher risk, you may be offered further testing or a detailed ultrasound.
Anatomy Ultrasound (18–22 weeks)
What it is: A longer, detailed ultrasound where the sonographer looks closely at the baby’s growth and development.
Why it’s done:
- Checks all major organs (brain, heart, kidneys, stomach).
- Looks at the baby’s spine, limbs, and face.
- Confirms placenta location and amniotic fluid levels.
- Often, this scan is when you can find out your baby’s sex, if you want to know.
What results might mean: For most families, it’s a happy milestone. Occasionally, if something isn’t clear (due to the baby’s position, placenta placement, or growth patterns), you may be asked to come back for another scan.
Third Trimester (24–36 weeks)
Glucose Screening (24–28 weeks)
What it is: A blood test after drinking a sweet orange drink.
Why it’s done: Screens for gestational diabetes, which happens when pregnancy hormones make it harder for your body to manage blood sugar.
What results might mean: If your blood sugar is higher than expected, you’ll be asked to do a longer test (glucose tolerance test). Gestational diabetes can usually be managed with diet, exercise, and sometimes insulin, and your care team will guide you.
Repeat Bloodwork (around 28 weeks)
What it is: Another blood draw.
Why it’s done: Checks your iron levels again and screens for antibodies if you’re Rh negative. If you are, this is when Rh immune globulin is usually offered.
What results might mean: Low iron may mean supplements. Antibodies might mean closer monitoring.
Group B Strep (GBS) Test (35–37 weeks)
What it is: A swab of your vagina and rectum — quick and usually done in your provider’s office.
Why it’s done: Screens for a type of bacteria that many people carry naturally but can be passed to baby during birth.
What results might mean: If positive, you’ll be given IV antibiotics during labour to reduce the chance of passing GBS to your baby.
Additional Ultrasounds (as needed)
What it is: Sometimes your provider may suggest more ultrasounds later in pregnancy.
Why it’s done: To check growth, amniotic fluid, or placenta health if there are concerns (such as high blood pressure, gestational diabetes, or baby measuring small).
What results might mean: Often just reassurance. If something unusual is found, your care team will discuss monitoring or birth planning.
Questions to Ask Your Care Provider
- Is this test routine or optional?
- What will this test tell me?
- How accurate is it?
- What happens if the results are unusual?
- How might this change my care or birth plan?
Final Thoughts
Prenatal tests and screenings are offered as part of routine pregnancy care in Ontario, but you always have a choice. Understanding what each test is for — and what results might mean — helps you make decisions that align with your values and your family’s needs. At Balancing Birth to Baby, we’re here to support you with evidence-based information and compassionate care every step of the way.
