Prenatal blood tests are usually done during your pregnanc​y visits​. 

Full Blood Count 

This measures your hemoglobin levels and enables doctors to detect anemia (low levels of red blood cells that carry oxygen in your body). The most common cause of anemia is iron deficiency and you may be prescribed iron supplements. 

This test will also enable doctors to screen for thalassemia​, an inherited genetic condition that may be transmitted to your ​​baby (read Thalasse​mia Tests​). 

Though less common, your baby may be severely affected if your partner is affected as well. More blood tests such as hemoglobin electrophoresis and DNA tests may be performed to confirm this diagnosis. 

Blood Typing 

This tells us several things about your blood. Firstly, it shows which main blood group you belong to (A, B, O or AB). 

Secondly, it helps to determine your Rhesus (Rh) status. You may be Rh positive (majority) or Rh negative (minority). 

If you happen to be Rh negative, you may require further injections (Rhogam) during the course of your pregnancy to prevent harmful antibodies from being produced that may harm your baby. Your doctor will discuss this in greater detail should you require this. 

​Hepatitis B Screen 

Hepatitis B​ infection is usually asymptomatic. For the mother, it may affect the liver function and will require long-term follow up for any deterioration or cancer change in the liver. This infection can be transmitted to the baby during the birth process. 

An immunisation regime can be started for your baby to reduce this chance of transmission and help prevent your baby from being affected. This minimises the chance of them developing liver dysfunction and cancer in later years. 

Note:​

​​If your are a Hepatitis B carrier, a Hepatitis B vaccine and antibodies will be administered to your child immediately after delivery. 

Syphilis Screen 

Fortunately, this sexually transmitted disease is now rare. However, it is still routinely done as early treatment with antibiotics may prevent stillbirth or deformities. 

HIV Screen 

The Human Immunodeficiency Virus​ (HIV) is the virus that causes AIDS (Acquired Immunodeficiency Syndrome). This can affect the immune system and cause eventual death. 

If the mother is found to be HIV positive, this can be transmitted to the baby during birth and breastfeeding. Through proper treatment with medications, Cesarean section and avoidance of breastfeeding, the risk of transmission can be reduced to less than 1%. 

Rubella / German Measles Screen (not routinely done) 

Most of the local women would have been vaccinated against this condition when young. If you are immune, you and your baby should be protected even if you come into contact with someone who has a rubella ​infection during your pregnancy. This is discussed in greater detail in the article Pr​​​​e-Pregna​n​cy Vaccination​.

If the tests indicate that you are not immune, you will be offered a vaccination in the postnatal period. 

Oral Glucose Tolerance Test (OGTT) 

This tests for diabetes ​mellitus in pregnancy and will require you to fast overnight. A fasting blood specimen is taken. 

You will need to drink a glucose ​solution before measuring your blood glucose levels again two hours later. 

It is considered abnormal if the glucose levels are above a certain level. 

Normal OGTT values: 

  • ​Fasting glucose level – less than 5.5 mmol/L 

  • 2-hour glucose level – less than 7.8 mmol/L 

The following group of patients may need OGTT: ​

  • A​bove 35 years of age 

  • Persistent glucose in the urine on at least two episodes 

  • Obesity (weight >80 kg) 

  • On long term steroids 

  • A family history of diabetes in first degree relatives 

  • A past history of diabetes in pregnancy 

  • A past history of big babies ( >4 kg) 

  • Suspected macrosomia (i.e. the baby is considered big for what is expected at the gestational age) 

  • History of unexplained stillbirth or bad obstetric history

Note:

If any abnormality is found, you will need to discuss it with your obstetrician.

Acknowledgement

Source: Dr TAN Thiam Chye, Dr TAN Kim Teng, Dr TAN Heng Hao, Dr TEE Chee Seng John, The New Art and Science of Pregnancy and Childbirth, World Scientific 2008. ​

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