Blood tests you can expect at your first prenatal appointment
Blood tests are a routine part of your prenatal care. When you go for your
initial visit either with your family doctor, OB, or your midwife, you'll be asked to give some blood. This is to check your blood group and whether you are Rhesus positive or negative, your hemoglobin level, and your immunity to German measles (Rubella). Your blood is also tested for syphilis, and hepatitis B. All pregnant women are now offered the test for
HIV/AIDS, but you don't have to have it if you don't want to. These initial blood tests are very important because they give you and your caregivers important information about your health and any possible problems you might have during your pregnancy.
Although in the past your age influenced what screening tests you were offered, according to the Society of Obstetricians and Gynaecologists of Canada and the Canadian College of Medical Geneticists,
all women, regardless of age, should be offered prenatal screening (it's up to you whether you want it). The results of initial blood tests to screen for possible genetic abnormalities, and not your age, will guide whether you are offered more invasive screening that can tell you more.
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At some point in the first trimester of your pregnancy, between 11 and 14 weeks, you may be offered genetic screening tests, either a variation of the integrated prenatal screening (IPS), or the first trimester screening (FTS), depending on where you live and what is available in your area. These tests do vary in accuracy, but all tests offered to you must be considered at least 75 per cent accurate, with a 3 per cent margin of error to be used, according to current guidelines
(SOGC 2007). Depending again on availability in your area, you may do these blood tests in conjunction with an
ultrasound, known as the
nuchal translucency ultrasound. The blood tests measure markers in your blood that can tell you what your risk is of carrying a baby with certain abnormalities, such as
Down syndrome.
If you are
Rhesus negative, which is tested at your initial visit, you'll likely be given a Rhogam shot around 28 weeks. Before that, your blood will be tested for antibodies around 28 weeks. You might also receive a Rhogam shot earlier in the case of a miscarriage or any prenatal bleed, and in case of an accident, such as a car accident or other accident causing trauma to you abdomen. And you'll get the shot when you have an amniocentesis or CVS.
Blood group
It's important to know your blood group in case you need a transfusion during pregnancy or labour. Blood group O is the most common; groups A, B, and AB are less so.
Rhesus (Rh) factor
Your doctor and midwife need to know whether you are Rhesus positive, which means that you have a certain protein on the surface of your red blood cells, or Rhesus negative, which means that you don't. If you are Rhesus negative and your partner is positive, there's a good chance that your baby will be Rh positive. In this case, your body might produce antibodies which start to destroy his red blood cells. (Read more about
what it means to be Rhesus-negative.)
Iron levels
A blood test can tell you if your hemoglobin levels are low, which is a sign of
anemia. If you're anemic, your doctor or midwife will talk to you about the best foods to eat (such as lean meat and spinach) to boost your iron stores. You might also be prescribed iron supplements. Your hemoglobin levels will be checked in your initial blood tests and with the glocose tolerance test in your third trimester. If you suffer a lot from
fatigue at any point during pregnancy, your doctor might (but won't necessarily) arrange for a blood test earlier to see if you are anemic.
German measles (rubella)
Most pregnant women are immune to
German measles because they've either been vaccinated against it or they've had the disease as a child. If you aren't immune, you'll be advised to avoid anyone who has or might have the infection. This is because if you catch German measles during pregnancy, your baby's heart, sight, and hearing could be seriously affected. You will also be given a Rubella booster after your baby is born.
Hepatitis B
You could be a carrier of the
hepatitis B virus and not even know it, so a blood test is often the only way to find out for certain. If you pass the disease on to your baby either before or after he is born, his liver could be seriously damaged. Babies at risk of catching the hepatitis B virus from their mothers can be given injections of antibodies as soon as they are born to protect them.
Syphilis
This sexually transmitted infection is fairly rare nowadays, however it is on the rise. If you have it and it isn't treated during pregnancy, it could cause abnormalities in your baby. The blood test for syphilis, called the VDRL, is, in general, an accurate test, but it can sometimes produce a false positive result, particularly if the woman being tested has
lupus.
Toxoplasmosis
If you're particularly anxious that you might be at risk of
toxoplasmosis -- an infection spread through cat feces and undercooked meat -- you could ask your doctor whether you can have a blood test for it, although it's unusual in this country for toxoplasmosis testing to be carried out. Severe cases of the infection can stunt the growth of the baby in the womb, and cause miscarriage and premature labour.
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