Pregnancy and HIV

The virus that causes AIDS, HIV, can be transmitted from an infected mother to her newborn child. Without treatment, about 20% of babies of infected mothers get infected.

Mothers with higher viral loads are more likely to infect their babies. However, no viral load is low enough to be “safe”. Infection can occur any time during pregnancy, but usually happens just before or during delivery.

The baby is more likely to be infected if the delivery takes a long time. During delivery, the newborn is exposed to the mother’s blood.


The viral load test measures the amount of HIV virus in your blood. There are different techniques for doing this:

  • The PCR (polymerase chain reaction) test uses an enzyme to multiply the HIV in the blood sample. Then a chemical reaction marks the virus. The markers are measured and used to calculate the amount of virus. Roche produces this test.  
  • The bDNA (branched DNA) test combines a material that gives off light with the sample. This material connects with the HIV particles. The amount of light is measured and converted to a viral count. Chiron produces this test.

The PCR test results are often different from the bDNA results for the same sample. Because the tests are different, you should stick with the same kind of test (PCR or bDNA) to measure your viral load over time.

Viral loads are usually reported as copies of HIV in one milliliter of blood. The tests count up to about 1.5 million copies, and are always being improved to be more sensitive. The first bDNA test measured down to 10,000 copies. The second generation could detect as few as 500 copies. Now there are ultra sensitive tests that can detect less than 5 copies.

The best viral load test result is “undetectable”. This does not mean that there is no virus in your blood; it just means that there is not enough for the test to find and count. With the first generation test, “undetectable” could mean 9,999 copies. “Undetectable” depends on the sensitivity of the test used on your blood sample.

Drinking breast milk from an infected woman can also infect babies. Mothers who are HIV-infected should not breast-feed their babies.

Provided by ArmMed Media
Revision date: June 20, 2011
Last revised: by David A. Scott, M.D.