Placental Ruptures Carry HIV to Fetus

Researchers have found that a large maternal enzyme (placental alkaline phosphatase, or PLAP) is too large to pass the intact placenta, which means that if it is found in umbilical vein blood, microtransfusions have occurred during labor and it is these that are responsible for carrying HIV to the infant during labor.

About 25-35% of mothers who are HIV-positive pass the virus on to their babies in the absence of any prophylaxis, and about half of these infections occur at birth. However, the mechanism responsible has not been well understood. It was widely thought that perhaps the mother passed the HIV to the infant as the infant passed through the birth canal.

When the researchers discovered the microtransfusions, they decided to test their hypothesis that the microtransfusions would enable HIV to reach the infant. They compared 149 HIV-positive women to all cases of in-utero and intrapartum mother-to-baby transmission in a larger group of HIV-infected mothers. The results showed that cord blood was significantly associated with intrapartum transmission. For emergency cesareans, no association was found, although data suggested reduced risk. No association was found between PLAP in the cord blood and in-utero mother-to-child transmission. The findings were reported in the November 21, 2005, online edition of the Public Library of Science Journal PLoS Medicine.

The researchers suggest that measures such as sanitizing the birth canal before delivery is unlikely to prevent HIV transmission from mother to infant. "It looks like direct mother-to-child blood mixing occurring during labor leads to infection,” said Steven Meshnick M.D., Ph.D., of the University of North Carolina (Chapel Hill, USA).




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