Understanding the blood tests you need during pregnancy
Blood tests are a routine part of antenatal care. A variety of blood tests are done by doctors and healthcare providers at various stages of the pregnancy in order to check on the mother’s health and to avoid problems for the baby.
What are the routine blood tests for a pregnant mother?
Full Blood Count (FBC):
A full blood count (FBC) is done to detect and cure anaemia prior to delivery. This will also avoid the need for blood transfusion during delivery. From the blood indices, one can also rule out the possibility of Thalassaemia or sickle cell anaemia. Those considered at risk will be offered a specific blood test for confirmation. If you are found to be a carrier of an inherited blood condition then the father of your baby will also be offered the screening.
Blood Group :
A blood group test will also be conducted to prepare for the possibility of blood transfusion during childbirth and to detect the presence of abnormal antibodies that may harm the baby.
Rhesus Factor :
A Rhesus Factor blood test will be done to detect and identify a rhesus negative mother and to avoid rhesus isoimmunisation which may harm the baby. If you are rhesus negative and your partner is rhesus positive your baby may be rhesus positive. This is usually not a problem in your first pregnancy, but may affect your next baby. This is because, after your first birth, some of the rhesus positive baby’s blood may enter your own circulation and may result in the production of antibodies. If this happens and it is not treated, the mother’s blood can create antibodies to attack any positive blood, since it contains a ‘foreign’ component. Therefore, if your next baby carries a rhesus positive blood, those antibodies can cross the placenta and cause the destruction of your baby’s red blood cells. This can be harmful to your baby and cause a condition known as haemolytic disease of the newborn, which can lead to anaemia and severe jaundice.
If you are rhesus D negative, you will be offered anti-D injections within 72 hours of delivery to prevent the formation of the rhesus D antibody.
Rubella Antibody Test :
The Rubella Antibody test is conducted to check if the mother is immune to the Rubella virus. When a mother is not immune or is susceptible to the Rubella infection, there is a high risk that the baby may be born with deafness, blindness or other problems known as the congenital Rubella syndrome. Avoidance of contact with someone who is suffering from the Rubella infection is advisable and Rubella immunisation is recommended after delivery for mothers who are not immune.
Syphilis Test :
The Syphilis test will be carried out to detect if the mother is suffering from Syphilis. Treatment can be given during pregnancy to prevent the baby from being affected.
Hepatitis B :
A mother who is infected will be given advice to prevent the transmission of the virus to others including her baby. A baby born to a mother infected with Hepatitis B will require both, the Hepatitis B vaccination as well as the immunoglobulin (antibodies) injection at birth to prevent the baby from suffering from the condition.
HIV Test :
This is an informed test. A mother who is HIV positive can infect her baby in the womb, during childbirth or through breast milk. Therefore, if the HIV status is known, steps can be taken to reduce the risk of transmission to the baby both before and after birth.
What are the other blood tests that can be done during pregnancy?
HbA1C (glycated haemoglobin) Test:
The HbA1C Test is conducted to detect overt diabetes in women who are at risk so that appropriate treatment can be administered to avoid the complications of diabetes during pregnancy.
Modified Glucose Tolerance Test:
This test is offered to pregnant mothers who are at risk of gestational diabetes (diabetes that only occurs when one is pregnant). These include :
- Women who are overweight (BMI of 34 or above)
- Women who have given birth to a large baby before (4kg or more),
- Women who have a close family member with diabetes,
- Women who have had gestational diabetes before.
If left untreated, gestational diabetes may contribute to an increased risk of miscarriage or a large baby. Newborns may be at risk of birth injuries, jaundice, low blood sugar and developing obesity or diabetes in later life.
Gestational diabetes can be controlled with lifestyle measures such as diet and exercise or with medications if needed.
Serum Iron and Ferritin Level:
The Serum Iron and Ferritin level test can be conducted in order to decide if the pregnant mother requires additional iron supplement besides the routine prenatal vitamins and minerals prescribed.
Toxoplasma and Listeriosis Tests :
This is done only in women who are highly susceptible to these infections. Both infections can result in miscarriage, stillbirth or severe deformities in the newborn if contacted during pregnancy.
First Trimester Biochemical Screening for Down’s Syndrome :
This is an optional test that is normally done along with the ultrasound examination of foetal nuchal translucency (an area behind the neck, beneath the skin) and nasal bone. It is usually performed between the 11th and 13th+6th weeks of pregnancy. This test measures Free β HCG and PAPP-A hormonal levels in the woman’s body. The detection rate for Down ’s syndrome is nearly 95% when the ultrasound scan and hormonal level test are combined.
Non- Invasive Prenatal Testing (NIPT):
This is a screening where the cell free DNA from the plasma of the pregnant woman is tested for aneuploidy. This test cannot be offered to women with multiple pregnancies. It is also not recommended as a screening for women who are at low-risk of having Down’s syndrome babies. It offers a detection rate of >99.9% for Down’s syndrome, Trisomy 18 and Trisomy 13 with a false positive rate of less than 5%. Those who tested positive should be offered invasive diagnostic tests for confirmation of the test results. NIPT can be performed after nine weeks of pregnancy.
NIPT is recommended for pregnant women who meet the following criteria :
- Maternal age of 35 years or older at delivery
- Ultrasonographic findings indicating an increased risk of aneuploidy
- History of a prior pregnancy with a trisomy
- Positive test result for aneuploidy, including first trimester, sequential, or integrated screen, or a quadruple screen
- Parental balanced robertsonian translocation with increased risk of foetal Trisomy 13 or Trisomy 21.
Second Trimester Screening Test for Down’s Syndrome (Double test, Triple test, Quadriple test):
This is another optional test done for the screening of Down’s syndrome. It is usually done between the 15th to 18th week of pregnancy. This test measures the level of two to four hormones (β HCG, alpha feto-protein and estradiol, inhibin A). The detection rate of this test is about 45% to 75%. If the test indicates a relatively high risk for Down’s syndrome, the woman will be offered invasive tests such as amniocentesis in order to detect if the baby is affected with Down’s syndrome. An abnormal level of alpha feto-protein might indicate the presence of neural tube defects, such as spinal bifida. Additionally, a detailed ultrasound examination of the foetus with emphasis on the head and spine would be offered to detect such abnormalities.
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This article was originally featured in Mummy’s Secret 3 – Your comprehensive guide to a healthy pregnancy.
Written by Dr. Yap Moy Juan, Consultant Obstetrician & Gynaecologist, Fetal Medicine & Gynaecology Centre; MBBS (MAHE) MRCOG (UK)
Dr. Yap received her post graduate qualifications from the Royal College of Obstetrician and Gynaecologist (FRCOG), United Kingdom. Prior to that, she received her undergraduate degree from the Manipal Academy of Higher Education in India. She has served as a specialist in Obstetrics and Gynaecology at Hospital Seremban and is currently based in the Fetal Medicine and Gynaecology Centre. She holds a special interest in the field of fetal medicine, subfertility, menopause and obstetrics medicine.
