The virus that causes AIDS is taking another step toward being manageable, and HIV-positive, pregnant women can now lower the risk of giving the virus to their babies to one or two percent.
"There's really no reason for them not to have a child," said Dr. Susan King, a pediatric infectious disease specialist at the Hospital for Sick Children in Toronto. "With good management of the mother's health, the rate can be down to two percent or one percent," Dr. King said. "That's getting close to the risk of congenital abnormality in the normal population," which is about three percent. "That's the order of magnitude you're looking at."
For HIV-positive women who have no symptoms, the transmission rate is about 20 to 25 percent. In 1994, researchers found that giving AZT, an antiretroviral, alone to such women starting before childbirth reduced the transmission rate to about eight percent. Subsequent studies showed that Cesarean sections reduced the rate further by lowering the infant's exposure to the mother's body fluids. The transmission rate for Cesarean section plus AZT drops to two percent, King said. Furthermore, breastfeeding was found to be clearly dangerous, leading on its own to a transmission rate of about 14 to 29 percent -- it is now strongly discouraged.
New studies show that the strongest predictor of transmission is the amount of virus in the mother's blood -- or the viral load. And that is now the prime focus of managing pregnant HIV-positive women, King said. "For most women that means being on combination therapy."
If the viral load can be dropped to the point where the virus is undetectable, "there is virtually no transmission," King said. And if the viral load is undetectable, a Cesarean section probably offers no additional benefit.
During pregnancy, women are advised to avoid medications and this raises the question of risk to the baby. Currently, it is unclear if there is a significant danger, King said. Children who were exposed to AZT around childbirth have been followed for five years and have no effects, she said. However, a study in France found that children exposed to both AZT and 3TC (another antiretroviral drug) seem to have a slightly higher than expected incidence of mitochondrial metabolic abnormalities. These abnormalities are defects in the body's chemical processes and the diseases associated with them can be severe.
"We've reduced the transmission rate from 25 percent to probably about one percent," King said. "We have a huge health benefit. And we possibly have a small risk of toxicity to some of the drugs. But if we're struggling to find it, it's clearly small."
One of medicine's goals is to eliminate HIV in children, and that may be feasible. One key step is to offer HIV testing to all pregnant women. "If you test everybody in pregnancy, then most (infected) people would be highly motivated," King said.
But another, more difficult requirement is to ensure that a social structure is in place to allow women to continue to follow therapeutic requirements. That will reduce transmission before and around the time of childbirth. But the child's well being continues to be an issue after that time, and long-term social support for the mother is necessary to ensure she continues to take her medicines.
"It's pretty pointless if we can prevent transmission, and the child is going to be orphaned because the mother doesn't have access to therapy afterwards," King said.
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