February 16, 2010

Viral Load Throughout Pregnancy Associated With HIV Transmission Risk

Viral load should be kept as low as possible throughout pregnancy, not just immediately before delivery, in order to minimize the risk of mother-to-child HIV transmission (MTCT), according to a French study published in the February 15 issue of Clinical Infectious Diseases and reported by aidsmap.

In developed nations such as France and the United States, the rate of MTCT has dropped substantially during the past 10 years, from roughly 8 percent in the early 1990s to about 1 percent today. The decline is mainly due to the widespread use of combination antiretroviral (ARV) therapy by HIV-positive pregnant women.

Though 1 percent is a tremendous improvement, it is not perfect. A small number of transmissions can occur when the mother’s viral load is below 500 copies at the time of delivery—the point at which MTCT is most likely to occur.

In turn, Roland Tubiana, MD, of the Hôpital Pitié Salpêtrière and his colleagues with the French Perinatal Cohort set out to better understand the risk factors for these “residual transmissions.”

The researchers compared a group of women who received ARV during pregnancy and had viral loads below 500 copies at the time of delivery. Nineteen of the women included in the analysis transmitted the virus to their infants (cases), whereas 60 did not (controls). None of the women delivered prematurely or breast-fed their infants after birth—both risk factors for MTCT.

According to aidsmap, a number of important differences were noted between the women who transmitted HIV to their infants and those who did not.

Only 16 percent of cases were taking ARV therapy before pregnancy compared with 45 percent of controls. In addition, 37 percent of transmission cases reported adherence problems during pregnancy, compared with 12 percent of controls. Both differences were statistically significant—too great to have occurred by chance.

Viral load during pregnancy differed significantly between the women who transmitted and those who did not. For example, none of the cases had viral loads below 500 copies for the entire duration of their pregnancy compared with 40 percent of the control mothers. And during the 30th week of pregnancy—the beginning of the third trimester—42 percent of cases had a viral load above 10,000 copies, compared with 11 percent of those who did not.

The researchers also found that 38 percent of transmission cases occurred at some point during pregnancy, not at the time of delivery. This was documented by checking for HIV DNA—as opposed to HIV RNA—at the time of delivery.

A very small number of women (0.4 percent) had a viral load below 50 copies but still transmitted HIV to their infants. Unfortunately, the researchers write, this confirms “that there is no threshold under which no residual transmission can occur.”

Still, the researchers argue that these findings offer tremendous insight. “HIV load during pregnancy should be monitored closely in order to take measures soon enough, such as reinforcing adherence, therapeutic dose adjustment, or switching for efficient antiretroviral therapy combinations,” they write.

NEW! Scroll down to comment on this story.

Previous Comments: