The risk of an HIV-infected mother passing the virus along to her baby during delivery nearly doubles if more than four hours pass between the time of water breaking and birth, a new study reported Thursday.
Writing in The New England Journal of Medicine, researchers with the Women and Infants Transmission Study suggested that the duration of exposure to maternal fluids is a more significant risk factor than the type of fluids (blood vs. amniotic fluids) or even the manner of delivery.The findings could be vital for the relatively small number of children whose HIV-positive mothers don't take the drug AZT during pregnancy or show resistance to the drug. Taking the drug during pregnancy usually lowers the risk of infection.
In those cases, "consideration should be given to performing caesarean section if the duration of ruptured membranes appears likely to exceed four hours," wrote the team headed by Dr. Sheldon Landesman, from the State University of New York Health Science Center at Brooklyn in New York City. They caution that evidence is still being gathered in other studies about how effective this step is in preventing mother-to-child transmission.
Two other obstetricians, Drs. Daniel Landers and Richard Sweet of Pittsburgh's Magee-Womens Hospital, in an editorial commenting on the study, said doctors should keep this increased risk in mind and avoid some standard birthing practices, such as intentionally rupturing membranes to speed labor, in women that are known or suspected to be HIV-positive.
But while "every effort should be made to shorten the time between the rupture of membranes and delivery," this does not mean that delivery "should be effected at or before four hours by whatever means necessary" that might increase other risks to mother and child, they added.
Some 7,000 HIV-infected women are reported to give birth each year in the U.S. Without treatment, about a quarter of them transmit the virus to their children. Taking AZT can reduce this risk by as much as two-thirds.
The researchers in the latest study said they have no evidence that the four-hour window applies to women taking AZT, because they looked at infection rates among women giving birth five years ago, several years before the preventive therapy was routine.
They studied infection rates of 525 infants born at hospitals in New York; Chicago; San Juan, Puerto Rico; and Massachusetts. Looking back three years after delivery, the researchers found that the ratio of babies infected rose from 14 percent to 25 percent when they were delivered more than four hours after the rupture of their surrounding membranes.
Another study published last week in the British journal Lancet involving women in Malawi found that washing the birth canal with a mild soap solution before delivery lowered the risk of transmission from 39 percent to 25 percent among women who delivered more than four hours after membranes broke.