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  Antenatal Blood Investigations

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To improve the pregnancy outcome, women are advised to have antenatal checkup soon after confirmation of pregnancy. During the first antenatal visit, medical staff will measure the body weight and blood pressure, test for urine protein and sugar, perform physical and vaginal examination, and offer the following blood tests to the pregnant women: 1. Blood grouping The four main blood groups are O, A, B and AB. 2. Haemoglobin and Mean Cell Volume These tests help to find out whether the pregnant mother has anaemia and to give clues to the types of anaemia. Thalassemia is the commonest hereditary blood disorder. Eight percent of the local population are thalassemia carriers. Most of these carries do not have symptoms, and only a small proportion may be mildly anaemic. When both parents are thalassemia carriers, there is one quarter chance of their babies getting 'Major' type of Thalassemia. It is a severe form of anaemia that may cause the death of the fetus or the necessity of life-long blood transfusion and drug treatment of the newborn. Pregnant woman who has low MCV may have iron deficiency anaemia or may be a thalassemia carrier. Her husband should also have the MCV checked. When both have low MCV, further blood tests are required. If both parents are thalassemia carriers, doctor will advise them to check whether the fetus is suffering form 'Major' type of Thalassemia. If so, they can choose to terminate the pregnancy.

3. Rhesus (RH) Factor Rh factor is an antigen found in red blood cells. Individuals who posses this factor are classified as 'Rh positive' and those without it as 'Rh negative'. Majority of the Chinese population are Rh positive. When a Rh negative mother is having a Rh positive fetus, this may lead to haemolytic anaemia, oedema or even death of the fetus. Such mothers should have regular blood tests throughout the pregnancy to find out whether the fetus has been affected. 4. Rubella Antibody A woman who has received Rubella Vaccination or contacted Rubella before conception should have developed immunity, that is, having Rubella antibodies. This can protect her from contacting Rubella during pregnancy which may cause abnormalities of the fetus. If she does not have Rubella antibody, she should receive Rubella Vaccination after delivery to safeguard herself and the fetus against Rubella infection in the next pregnancy. 5. Hepatitis B Antigen Ten percent of the local population are carriers of Hepatitis B virus. Most of these carriers show no signs or symptoms of the disease. A mother who is a Hepatitis B carrier may transmit the virus to the infant at or around the time of delivery. Therefore, if the blood test is positive for Hepatitis B Antigen, that is, the mother is a carrier, the newborn should receive Hepatitis B Vaccination and Hepatitis B Immunoglobulin after birth so as to be protected against Hepatitis B infection.

6. Syphilis Untreated syphilis in pregnancy may cause abortion or congenital defects of the fetus such as blindness or deafness. Therefore, early detection and treatment are necessary. 7. Human Immunodeficiency Virus (HIV) Antibody Testing HIV can cause AIDS (Acquired Immune Deficiency Syndrome). The routes of transmission include sexual intercourse, blood contact or from an infected mother to her baby during pregnancy, delivery or breastfeeding. The transmission rate from an infected mother to her baby is 15-40%. Early detection and antiviral treatment can reduce the risk of HIV transmission from mother to child by two-thirds. Please contact medical staff if you have any queries concerning the above blood tests. Source of Information: Family Health Service, Department of Health Hospital Authority

 
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Last revision date: 01 September 2006