Being pregnant

Prenatal tests

Wondering what kinds of tests (scans, poking and prodding) you'll go through during your pregnancy? Here's our primer on prenatal tests

By Haley Overland
Prenatal tests

So it’s time for your 12-week ultrasound. Why are you having it? What are they looking for? How long will it take? Can you watch? Can you bring your partner? What about the 20-week ultrasound and all those other tests that moms-to-be have to take — amnio, glucose challenge, routine bloodwork? No need to look any further. Read on for our primer on prenatal tests. (Note: Your caregiver might require you take additional tests. This is a general list of what to expect. Talk to your caregiver if you have questions or concerns.)

Tests in first trimester

What to expect Your first ultrasound(s), blood and urine tests

When Weeks 11 to 13 (*dating ultrasound is done sooner)

Dating ultrasound Not everyone gets this scan but some caregivers offer a dating ultrasound if you’ve had bleeding in the first few weeks or had problems in prior pregnancies (miscarriages, etc.). You might also be sent for one to check your conception date and to make sure the pregnancy is progressing well.

Your 12-week(ish) ultrasound This scan (performed on the belly and sometimes vaginally—called a transvaginal ultrasound) in combination with a blood test will complete what’s called a “nuchal translucency test,” which estimates the likelihood that your baby will have Down sydrome by measuring the fluid beneath the skin of the back of your baby’s neck. If the test indicates a high likelihood, caregivers will recommend amniocentesis or CVS (Chorionic Villus Sampling), which are more invasive tests, but will give you accurate diagnoses. (Read about those tests below.)

The ultrasound technician will also measure the length of the fetus to give caregivers a more accurate estimation of your due date.

Feel free to bring your partner, friend or parent to this special event—they’ll love being there to watch your babe’s first video with you. Depending on where your scan is done (hospital, clinic, etc.), your partner might not be permitted to watch the entire scan (which usually doesn’t take too long if the baby is cooperating) but he’ll be called in toward the end to see baby.

First prenatal blood tests After your scan you’ll have blood taken. This blood test looks for:

• Down syndrome: A blood test is performed in combination with the first ultrasound to determine the likelihood your baby will have Down’s Syndrome. Specifically, caregivers test for abnormal levels of hCG (human chorionic gonadotrophin) and PAPP-A (pregnancy associated plasma protein).

• Blood type and Rh (Rhesus) factor: It’s important for your caregiver to know your blood type and Rh factor. If your Rh factor differs from that of your baby, you may have an immunological reaction to your baby’s blood. This is mostly an issue in subsequent pregnancies, since it is the antibodies created in the first pregnancy that are harmful. This test makes Rh Factor related problems preventable.

• Anemia: If you test positive for anemia, it means you don’t have enough red blood cells—typically because you are deficient in iron. Red blood cells are particularly important during pregnancy because they transmit oxygen to the fetus. Anemia is treated immediately upon detection with an iron supplement.


• Hepatitis: Many women have a liver condition known as Hepatitis B and don’t know it. It’s important to test for it during pregnancy because it can be transmitted to the fetus before or during the birth. If you are infected, your baby can be vaccinated immediately after the birth.

• Rubella (German measles): Although most Canadians have been vaccinated for the German measles in childhood, or even contracted the illness when they were children, the test is done anyway just to be sure you aren’t infected. If a woman in early pregnancy catches it, serious birth defects can occur.

• The VDRL: Pregnant women require a syphilis test because the disease can cause neurological damage to the baby or even stillbirth.

• Genetic disorders: If tests haven’t already been done, your doctor or midwife may request tests.

• HIV: An HIV test is included in this batch. If a test turns out positive, treatment can dramatically reduce the baby’s risk of acquiring the disease.

Urine tests Your urine will be tested at every prenatal visit to check for protein in the urine, which indicates pre-eclampsia—a manageable condition characterized by swelling and high blood pressure that risks reducing blood flow to the placenta.

Your sugar levels may also be tested to determine your risk for gestational diabetes.

Amniocentesis or Chorionic Villus Sampling If your nuchal translucency ultrasound shows a high likliehood of Down syndrome, your caregiver might suggest amniocentesis. This is a diagnostic test that involves extracting a sample of amniotic fluid from your uterus with a long hollow needle (as far away from the baby as possible) and testing it for indications of serious chromosomal abnormalities, such as Down syndrome, trisomy 18, Edwards syndrome, as well as neural tube defects such as anencephaly and spina bifida. The test can also tell you the sex of your baby, the Rh factor and the maturity of his/her lungs (which is useful if you show signs or have a history of premature delivery). The whole process takes about half an hour, usually with little discomfort except for some minor cramping post-procedure. Results take about two weeks to process.

Expectant moms who usually have this test are moms older than 35, women who have a family history of birth defects, women whose partners have a family history of birth defects, or women whose previous children were born with abnormalities. The test does come with risks—the earlier the amniocentesis takes place, the higher the risk of miscarriage. Talk to your caregiver.

Chorionic Villus Sampling (CVS) as an alternative to amniocentesis because it can be done earlier (between weeks 10 and 12). Like the amniocentesis, the test takes about half an hour and may be uncomfortable. The doctor either inserts a needle into your abdomen (after local anesthetic) or a thin tube or catheter through the vagina and cervix to get to the placenta. Through the needle or tube, the doctor extracts a sample of chorionic villi, or fingerlike growths in placental tissue, which harbour genetic information (even the sex of the baby). Results of the CVS are quicker to get.

Like the amnio, there is a risk of miscarriage. CVS has also been associated with other defects (though only if it’s performed before week 10).

Tests in second trimester

What to expect Your second-trimester ultrasound; the glucose challenge

When Around 20 weeks; around 26 weeks

Your 20-week(ish) ultrasound Yup, this is the ultrasound you’ve been waiting for—if you want to find out whether you’ve been schlepping around a wee boy or a wee girl. (P.S. Not all hospitals and clinics allow sonographers to share this info, so don’t be too shocked if they aren’t willing to divulge.) This ultrasound involves a complete “anomaly scan” (and we mean complete—everything from the nose to the heart’s chambers will be scrutinized) to make sure your baby is developing normally in all areas and that everything is a-OK. The technician will also scan the umbilical cord, placenta and amniotic fluid to see how the pregnancy is progressing. Don’t be surprised if you’re on the table for more than an hour—this scan takes a while to do thoroughly. You might even be rescheduled for another scan if baby isn’t cooperating.

Like your first ultrasound, some clinics don’t allow your partner in for the entire scan. Ask before you go in about the hospital or clinic’s policy. And don’t forget to ask for photos of your little one. (Tip from moms who’ve been there: Bring cash. Most hospitals charge a small fee for pics these days.)

Glucose Tolerance Test (weeks 24 to 28) You’ve no doubt heard about the orange pop test—this is the one they do to check for gestational diabetes. About three percent of pregnant women develop this condition (even though 15 percent of women will test positive for high glucose levels). It usually resolves itself post-pregnancy, but is important to keep under control during pregnancy (through dietary modifications and exercise or, rarely, insulin injections) so that the baby doesn’t get too big. You’ll have to take this test whether or not your routine urine checks show high levels of sugar—that’s pretty much the only symptom of gestational diabetes.

The test is a two-parter: First you gulp down a sickeningly-sweet orange beverage that tastes a lot like orange pop (but much sweeter and without the bubbles). Exactly one hour after the drink (this is a timed test—when they say an hour they mean an hour) you’ll go for a quick blood test. If high glucose levels are detected, you will be asked to return for a second test that involves fasting for six hours, drinking the orange beverage again and taking three blood tests in one-, two- and three-hour intervals. If two of the three levels are high, they’ll tell you that you have gestational diabetes and treatment will commence so you can go on to have a healthy pregnancy and baby.

Tests in third trimester

What to expect Possible follow-up ultrasounds if directed by your caregiver; Group B Steptococci (GBS)

When Any time; weeks 35 to 37

Your third-trimester ultrasound If your pregnancy is progressing normally you probably won’t be offered an ultrasound after the 20-week scan. Your caregiver might want you to have one if:

• you’ve had complications in previous pregnancies
• your blood pressure has been high
• you have diabetes (or gestational diabetes)
• the position of your placenta needs to be monitored (if your caregiver mentioned the possibility of placenta previa—or your placenta was too close to your cervix at your 20-week ultrasound—third trimester is when they check to see if the placenta has corrected itself)
• your caregiver is concerned about baby’s growth (whether she thinks baby is too big or too small)
• you’re carrying multiples

Group B Streptococci (GBS) Test To prepare for your baby’s delivery, your caregiver will take a swab of your vagina and rectum to check for Group B streptococci—a common bacteria that is harmless to mom, but potentially dangerous to baby. (This usually happens around week 36.) No need to worry—a third of pregnant women test positive for this bacteria. It simply means that your caregiver will administer antibiotics, either at the start of labour or when your water breaks, to protect the baby from contracting an infection.

This article was originally published on Aug 03, 2010

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