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HIV testing in pregnant women

In the US there are approximately 50,000 new cases of HIV infection per year. Of these, approximately 150 involve vertical transmission from mother to child whilst the mother was still pregnant. In Singapore the number of new cases of HIV reported in 2014 was approximately 118 per million resident population. In Singapore, between 2008- 2014, there were only 2 reported cases of vertical transmission with none occurring within the last 4 years.

Although we can see that vertical transmission makes up a small percentage of the overall infection rates, it represents an important and potentially avoidable number.

New recommendations from the US shows that if an HIV positive mother is given antiretroviral medications during pregnancy and delivery as well as to their newborn in the first few weeks of life, the vertical transmission rate is reduced from 25% to 2% or less. Further evidence also suggest that starting antiretroviral medications early helps to reduce the rate of HIV transmission through sexual intercourse, which itself is also an important issue.

Hence, we can see that accurate and early identification of HIV would not only be beneficial to the mother but also to her child.

Several tests are available for HIV;

  • 1) HIV RNA PCR – don’t worry about the full name of this test, it is quite a tongue twister. However, this is probably one of the best test, if not the best, as it is actively aims to culture the virus and give a quantitative value. This test will be conclusive 10 days after any potential exposure.
  • 2) Antigen/Antibody testing – this type of test is available as a rapid test with the results ready within 20 minutes. The antigen is a marker seen on the surface of HIV itself, which means it can be picked up at an early stage (usually 2-4 weeks after infection). The antibodies are the body’s immune response to the virus itself but this can take 6 weeks or more in order to manifest. This test is therefore conclusive at 28 days after any potential exposure.
  • 3) Antibody testing only – This would be the same as the above mentioned but only test for the antibody. It can pick up HIV as early as 6 weeks but only really conclusive at 12 weeks after any potential exposure.
  • 4) Western blot – This test is very old and not particularly accurate but it is still the recommended confirmatory test here in Singapore. Therefore this test is only used to aid confirmation, it should not be use for diagnosis.

Current Singapore guidelines recommend one of the first 3 tests for diagnosis and should they be positive, the western blot is recommended for confirmation. Current US guidelines, however, would recommend using one of the first 3 tests without using the western blot test.

All pregnant women should ideally be screen for HIV as early as possible during each of their pregnancies. This will aid in early diagnosis, followed by early treatment. There are some parties in the US that recommend opt out testing, meaning that all women should be tested unless they specifically choose not to be tested. Currently, no such policy exist in Singapore.

Another policy recommended under the US guidelines but is also not applicable to Singapore is that women who arrive at the delivery ward with an undocumented HIV status should have rapid HIV screening done unless she opts out.

Upon testing should a pregnant woman’s results be positive, they should be given to her in person with the implication of HIV infection and risk of vertical and horizontal transmission being discussed. At this point, further blood tests may be needed which include HIV viral load, CD4 white cell counts as well as other potential infectious diseases such as hepatitis B and C may be needed. Additional tests such as a full blood count, and baseline kidney and liver tests may be helpful. The women should then be referred to a specialist for ongoing care and the commencement of treatment as early as possible.

In summary, vertical transmission of HIV from pregnant mother to baby is an important and highly preventable issue. Thankfully, vertical transmission rates in Singapore are remarkably low, but this should not deter pregnant mothers from seeking early screening as early identification with rapid testing and subsequent confirmation is key to early treatment. This itself is one of the single most important factors in deciding transmission rate from mother to baby.


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