Routine Blood Tests: Communicable diseases

A Health Department Letter (HDL 52) issued in June 2002 recommended that human immunodeficiency virus (HIV) testing should be offered routinely to all pregnant women as part of their antenatal care. This test was introduced in Scotland in 2002 and forms part of the integrated programme of antenatal screening to limit risk for a number of communicable diseases (hepatitis B, syphilis and rubella as well as HIV).

The primary aim of screening women for these conditions is to ensure a plan for treatment and management for affected individuals and their babies. Tests for infection with HIV, hepatitis B and syphilis, and immunity to rubella, are carried out on serum obtained from a single blood sample taken at the first booking appointment. Occasionally a second blood sample may be required for technical reasons to confirm a test result.

Tests for HIV, syphilis and rubella are based on the detection of a specific antibody to each. The test for hepatitis B virus detects viral antigen in the same sample.

Human immunodeficiency virus (HIV)

The Human Immunodeficiency virus (HIV) is the virus that causes Aquired Immunodeficency Syndrome (AIDS).  HIV can be transmitted from a mother to her baby, the risk being 25% when no treatment is given. Detecting the HIV antibody in the mother’s blood at any stage of pregnancy, but preferably early on, can help to reduce transmission to less than 2% through antiviral treatment and taking appropriate measures during delivery.

All positive test results indicating a possibility of HIV are confirmed by retesting, using a different test method. The combination of two tests produces high accuracy with minimal risk of false results. HIV antibody tests exceed the performance of most other infectious disease tests in both sensitivity and specificity. Although these tests are very sensitive, there is an interval known as a ‘window period’. This is the period between the onset of infection with HIV and the appearance of detectable antibodies to the virus. This period is usually less than a month, however, it may be longer for some individuals. It is important that women are aware that despite being given a negative test result, it could be that antibodies are not yet present and therefore the result given could be false. If a woman feels she has been or continues to be at risk of exposure to the virus, further three-monthly testing should be offered throughout pregnancy.

Hepatitis B

Hepatitis B infection can be transmitted from mother to infant.  Hepatitis B is a virus that infects the liver.  Many people with Hepatitis B have no symptoms at all and don't know they are infected.  Others have flu-like symptoms and yellowing of the skin (jaundice).  Hepatitis B infection can only be identified by a blood test.

Many adults with hepatitis B recover fully but about one in 10 adults can remain infectious and spread the infection to others.  About one in five of this group could develop serious liver disease (hepatocellular carcinoma) later in life. 

Perinatal transmission of the hepatitis B virus can occur if the mother has an acute infection in pregnancy or if she is a chronic carrier of hepatitis B.

A full immunisation course will protect babies from the hepatitis B virus, this consists of:

  • the first dose at birth
  • the second dose at one month
  • the third dose at 2 months
  • the fourth dose at 12 months

if the mother has hepatitis B, the baby will need a blood test at 12 months to check the immunisation has worked.  For children still at risk, a fifth dose will be given hen they are 3 years 4 months old with their routine immunisations.

Syphilis

Syphillis is passed on though having sex and is uncommon these days.  Syphilis infection can have consequences for both mother and infant, but detection of infection early in pregnancy allows appropriate antibiotic treatment to prevent transmission. About 50% of infected mothers will be asymptomatic and the causal agent, treponema pallidum, can cross the placenta at any stage of pregnancy. However, maternal antibiotic therapy can prevent nearly all congenital syphilis.

Rubella

Rubella infection used to be a common mild infection of childhood, and is characterised by a short period of illness and a rash. If rubella is contracted during the first trimester of pregnancy it can lead to severe abnormalities in the baby, including deafness and eye and heart disease. The incidence has been largely reduced by immunisation of children and young women before conception, but there is a continuing need to look for evidence of immunity in pregnant women to ensure congenital rubella syndrome is very unlikely in Scotland.


Find more information on Clinical Standards for Pregnancy and Newborn Screening.

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