Prenatal Investigations

When you're pregnant, prenatal tests give you information about your health and your baby's.
Group B streptococcus (GBS)


There is a high demand for iron during pregnancy and some women may become anemic. Hemoglobin (Hgb) is a test to make sure the blood is able to carry enough oxygen and iron. This test may also reveal certain clotting abnormalities or congenital blood problems.

If your hemoglobin or iron levels are low, your health care provider may ask you to take an extra iron supplement. Iron is safe in pregnancy and can be bought over the counter.
  • Is best absorbed on an empty stomach
  • Do not take iron at the same time as calcium, antacids, your regular prenatal vitamin or dairy products
  • Can cause cramps, nausea and diarrhea
  • You can take it with a small amount of food
  • Taking your iron with vitamin C can help your body absorb the iron better

    What foods are good sources of iron?
                      What foods are food sources of iron? Learn more on the Dietitians of Canada website.

Hepatitis B surface antigen (HbSAg)

This is used to identify people who carry the Hepatitis B virus. To prevent the transmission of the virus to the baby, we test all pregnant women. If a mother carries the virus, we would immunize the baby. If your partner or anyone living in your household is a Hepatitis B carrier, please let your health care provider know. Your baby will receive immunization to prevent him/her from getting this virus.

Rubella (German measles) antibodies

If you have antibodies for Rubella, it means you have been immunized or exposed to this virus in the past and you and your unborn baby will not get this disease. If you do not have antibodies, it means you are still susceptible to rubella. Rubella is harmful to the unborn baby. Avoid contact with people who are currently infected with rubella (this is not always possible as not all infected people have symptoms). You will be immunized after the baby is born to protect any future pregnancies.

This is a screening test for syphillis. It is done by law on all women delivering in Ontario. Recently it has become extremely rare to encounter a positive result.

Blood group and antibody screen 

A person's blood type is determined by the type of antigen attached to the blood cells. An antigen is like a marker on the blood cell. An antibody is something that your body makes against particular antigens to attack those cells that have that antigen.

There are four (4) different blood types: A, B, AB and O.
ABO Blood Group System
What is an antigen?
An antigen is any substance that causes your body to produce antibodies. In this case, antigens are what identify your blood cells as belonging to a certain blood type.
What is an antibody?

Antibodies are proteins made by the body to attach to and attack certain antigens.

Another major antigen is called Rh factor. If your blood has this antigen, it is Rh positive; if there is no antigen, then you are Rh negative. On average, only about 15% of people are Rh negative. It is also dependent on racial background.

During pregnancy, a small amount of the baby's blood may enter the mother's system. If the mother is Rh positive, this does not matter. If the mother is Rh negative and the baby is Rh positive, the mother's blood may react by forming Rh antibodies. These antibodies may then enter the baby's circulation and destroy the baby's red blood cells — this is known an Rh disease. Fortunately, this is preventable.

If you're Rh positive: no precautions are needed regardless of the father's blood group.

If you and the baby's father are both Rh negative: the baby will also be Rh negative, so no precautions are necessary.

If you are Rh positive and the baby's father is Rh negative: no precautions are necessary

If you are Rh negative and the baby's father is Rh positive: the baby may be Rh positive. To prevent Rh disease, you will be given Rh immunoglobulin (Rhlg). This immunoglobulin attaches itself to the baby's red blood cells (which contain Rh factor) and will be collected by your spleen; they are taken out of your circulation and no Rh antibodies will be formed to cause Rh disease.

Learn more about RH incompatibility on the Mount Sinai Hospital website.


See the patient information sheet on Rh immune globulin, often referred to as RhIG. Download: Patient information sheet on RH Immune Globulin  Rh immune globulin is a blood product recommended whenever there is a chance of an Rh negative woman forming antibodies.
When should I get Rhlg?
  • Anytime you have bleeding
  • At 28 weeks even if you have no bleeding
  • After delivery and prior to discharge if the baby tests Rh positive
  • In pregnancies complicated by trauma
  • After an ectopic pregnancies
  • After a miscarriage or stillbirth
  • After invasive procedures such as amniocentesis, chorionic villus sampling or ECV
Rh immunoglobulin does not affect the baby in any way during pregnancy and is a safe blood product.

Rh immunoglobulin does not affect the baby in any way during pregnancy and is a safe blood product. Learn more about when you need Rh immune globulin. Download: When you need Rh immune globulin

How should I get Rhlg?
Your health care provider will provide you with a requisition and a copy of your current pregnancy blood group and Rh results. Make sure to bring these documents to the hospital's Outpatient Lab on the 4th Floor South East. After you repeat your blood test for the antibody screen, please go to the Assessment Room (2S-177). A nurse will give you RhIg that was issued by the hospital Blood Bank.

To prevent delay when you come to the lab at 28 weeks, please bring a copy of your current lab documents from your health care provider. The lab hours are Monday to Friday 8 a.m. to 3 p.m. Please note if you do not bring your lab documents, the latest appointment is 1 p.m.
HIV testing

The HIV blood test can tell us if you have the virus that causes AIDS. It is recommended that all pregnant women be tested for the virus. It can take up to 10 years before a women who has HIV notices symptoms. She can still infect her baby with the virus during pregnancy, while giving birth or through breastfeeding. If the mother has the virus, the chance of this happening is about 21%. If the health care provider knows that a woman has the HIV virus, the mother is treated with medication during her pregnancy, as well as during labour. The baby can be treated after birth and this will lower the baby's chances of becoming infected with the HIV virus to 1%. If you are HIV positive, do not breastfeed.

Blood sugar

We do not recommend routine random tests for blood sugar levels. However, during pregnancy, the way the body handles sugars may be unusual (gestational diabetes). In an otherwise normal pregnancy, the elevated blood sugar levels usually return to normal levels after delivery.

There are various ways to screen for gestational diabetes. Your routine urine check at prenatal visits is one of them. At 24-28 weeks, you will have a 50 g glucose challenge test. A sweet drink is given, followed an hour later by a blood test for glucose. No fasting is necessary. If this test is abnormal, we would recommend doing a fasted 75 g glucose tolerance test.

Between 3–20% of pregnant women will be diagnosed with gestational diabetes.
Toxoplasmosis and CMV

The immune status may be tested on individuals under certain circumstances, as determined by your health care providers.


This is an illness also known as Fifth’s Disease or "Slapped Cheek Disease". Symptoms include a rash, fever, muscle/joint aches, headache, sore throat, itching, cough, diarrhea, nausea, vomiting, eye infections or no symptoms at all. These first symptoms last 2–5 days then may be replaced with a rash on the face called a “slapped cheek” rash. Joint pain is more common in adults than children. Children often feel better by the time the rash appears, and the rash may go away and come back with stress and exercise. Patients are usually considered infectious until they get the rash or joint pain.

Parvovirus is common in children, and most people have come into contact with parvovirus at some point in their lives, especially if they work with children. Half of all pregnant women are already immune which means that they are unlikely to get sick again. There is no treatment for it and most people get better on their own. If you think you have been exposed to parvovirus while pregnant, let your health care provider know.

If you develop an active infection in pregnancy, there is a small risk of the baby developing anemia, and you will have to be monitored with ultrasound. There is no increased risk of developmental or learning problems with a parvo infection.

You can lower your chance of getting parvovirus by proper hand washing and teaching your children to do the same. Avoid children who have an active parvovirus infection.
Varicella is a highly contagious disease more commonly known as chickenpox.
Varicella (Chickenpox)

Varicella is a highly contagious disease more commonly known as chickenpox. Symptoms include fever, feeling tired and a characteristic itchy blistering rash. Most pregnant women are immune to varicella which means they are unlikely to get sick from it again.

If you are not immune to varicella, you should avoid contact with anyone known to have varicella.

If you contact someone with varicella, go to the Assessment Room immediately
If you are not immune to varicella and think that you have been exposed to someone with varicella, go to the Assessment Room (2S-177) immediately. Do not wait until the next day.

If you are not immune to varicella and think that you have been exposed to someone with varicella, go to the Assessment Room (2S-177) immediately. Do not wait until the next day.

We can give you an immunoglobulin to block the virus. Varicella can be very dangerous for both the mother and the unborn baby. The varicella vaccine can be given to you after the pregnancy by your family doctor.

Group B Streptococcus (GBS)

Group B Streptococcus (GBS) bacteria can potentially be a serious infection for a newborn. More than 15% of pregnant women are GBS carriers in the vagina and rectum. It usually does not cause symptoms in the mother, but may occasionally cause a urinary tract infection. Rarely, babies born in this situation may develop a serious infection.

At North York General Hospital, guidelines are in place for identification and care of the expectant mother, whose newborn infant may be at risk of developing an infection from GBS.

Care of the mother: at about 36 weeks gestation, a swab from your vagina and rectum will identify the presence or absence of GBS. If this swab is positive, the expectant mother will receive intravenous antibiotics while in labour. This has been proven to reduce the likelihood of infecting the newborn.

Care of the newborn at risk of GBS infection: GBS can cause serious illness in a newborn. This infection usually occurs soon after birth. Infections that take place during the first week of life are called early onset and later onset infection is less than 3 months of age. These babies typically contract GBS from their mothers before or during birth. Premature newborns are more likely to develop GBS infections than full-term infants. The treatment of suspected infections before and after delivery does not entirely prevent the infection, but it can substantially reduce it. Treatment of early onset GBS does not prevent the late onset GBS due to different means of transmission of this infection.

Learn more about Group B streptococcus infection from the Society of Obstetricians and Gynaecologists of Canada. Download: Group B streptococcus infections flyer
Signs and symptoms of a baby with GBS
  • Fever
  • Excessive sleepiness
  • Irritability (inconsolable crying)
  • Vomiting
  • Breathing too fast

When to see your baby's doctor or midwife

Take your baby to the family doctor, paediatrician or midwife the day after you go home from the hospital if your baby has been discharged home before 48 hours of age. Remember to give the doctor/midwife the newborn record you received from the nurse before you left the hospital.

Contact your health provider if your baby becomes:

  • Very sleepy and difficult to wake up
  • More fussy than usual and unable to settle
  • More difficult to feed
  • Very jaundiced (skin turning yellow)
Go to the nearest ER if your baby:
  • Starts to breathe faster or seems to be having difficulty breathing If you think your baby may be ill, call Telehealth Ontario.
  • Becomes pale or skin starts to turn blue or purple
  • Develops a fever (temperature more than 37.5°C or 99.5°F under the armpit)

Not sure if your baby is ill?
Call Telehealth Ontario (1-866-797-0007).
Telehealth Ontario is a free, confidential service you can call to get health advice or information. A registered nurse will take your call 24 hours a day, 7 days a week.


You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider. If you have any specific questions about any medical matter you should consult your healthcare provider. If you think you may be suffering from any medical condition you should seek immediate medical attention. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information on this website.