HIV testing in pregnant women

Epidemiology Corner

September 24, 2004

HIV testing in pregnant women
Shirley Chan and Koya Davis

From 1981 through June 8, 2004, 2,032 children have been reported were born to HIV infected women in Houston and Harris County. Of these children, 291 were diagnosed as HIV infected, 515 have an undetermined status and the remaining 1,226 are seroreverters (HIV negative).

Perinatal transmission (from mother to child) of HIV can occur in three different ways: during pregnancy (intrauterine), during labor and delivery (intrapartum) or after delivery through breast-feeding (postpartum). Recent estimates of transmission risk indicate that 60-70 percent of the risk can be attributed to the birthing process (intrapartum), 20-25 percent is due to blood exchange during gestation (intrauterine) and 10-15 percent is due to breast-feeding (postpartum). Two studies have shown that antiretroviral therapies and caesarean section can reduce transmission risk from a high of 16-25 percent to less than 2 percent.

The use of zidovudine (AZT) and other antiretroviral drugs during pregnancy for HIV infected women, the regimen of zidovudine administered to newborn infants and the implementation of United States Public Health Service (USPHS) guidelines for universal HIV counseling and testing of pregnant women have all contributed to the dramatic decline (an estimated 70 percent decrease in the number of HIV infected children – Centers for Disease Control and Prevention 2002) in perinatally acquired HIV. The USPHS recommends that all health-care providers, as part of the standard battery of prenatal tests, offer HIV testing on a strictly voluntary basis to all pregnant patients. The state of Texas follows these guidelines by using the Opt Out Approach. This means that an HIV test will be administered to all pregnant women as a part of their routine tests, regardless of whether the examination occurs during gestation or at the time of delivery of the infant. The woman must be informed of the HIV test prior to testing and advised that the result of the test is confidential, not anonymous. The woman has the right to refuse HIV testing.

In response to the USPHS recommendations and state laws on HIV testing of pregnant women, physicians have increased their effort to screen patients during the prenatal period. As the number of women being screened has increased, the proportion of false-positive and ambiguous (indeterminate) test results has increased and the positive predictive value (an assessment of the reliability of positive tests) of the standard HIV test as used during pregnancy has decreased. To avoid misinforming patients about their HIV status, physicians need to be alert to the possibility of false-positive or ambiguous HIV test results and know how to verify an ambiguous or positive result. Some of the basic concerns doctors need to consider are: if the screening antibody is positive and the confirmation test is ambiguous or equivocally positive, how are we going to confirm whether the woman is truly infected? If HIV positivity cannot be proven using a diagnostic tool, is it wise to administer ZDV to mother and infant? What is the alternative?

While the legal and ethical ramifications of this issue are beyond the scope of this article, there are also practical questions of particular interest to the women involved. Women who understand the basic natural history of the disease, the risk of transmission, the different types of HIV tests and the possible test results can make better informed decisions about themselves and their babies. Information about HIV and HIV tests can be found on the Centers for Disease Control website at http://www.cdc.gov/hiv/dhap.htm. Information about HIV in Houston can be found on the HDHHS website at http://www.houstontx.gov/health -- Stay tuned for Part Two of this article - an interview with Dr. Hunter Hammill, a leading HIV obstetrician/gynecologist infectious disease specialist in Houston.