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An estimated one-third of HIV-positive women who smoke during pregnancy and do not take AZT may pass HIV on to their babies.

Researchers at Thomas Jefferson University, Philadelphia, and the New York State Department of Health have found an association between cigarette smoking and an increase in maternal-child HIV transmission. An analysis of 901 HIV-infected women on Medicaid and their babies delivered between 1988 and 1990 in New York, the state with the largest number of women and children with AIDS in the United States, showed that an estimated one-third of these women who smoked and did not take antiretroviral drugs like AZT passed HIV onto their children. Study results appear in the April issue of the Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology.

"In addition to contributing to poor birth outcomes, we know that nicotine is toxic to blood vessels and adversely affects the placenta, promoting premature rupture of the membranes surrounding the baby," explained Barbara J. Turner, M.D., principal investigator and professor of medicine at Thomas Jefferson University Hospital. "Our study shows that smoking may be especially dangerous for HIV-positive pregnant women, because its effects may increase the babys exposure to blood and other maternal secretions that contain the virus during delivery. For women who are not treated with antiretroviral medication and who have more advanced disease, smoking is associated with a greatly increased risk of maternal-child HIV transmission."

Researchers studied statewide Medicaid claims data from New York, which provided them with a large study sample since 60 to 80 percent of HIV-infected women in the state are on Medicaid. Researchers developed methods to match each woman to her child and then establish the HIV status of both mother and baby. The entire study was conducted without the Jefferson researchers having any information that could be linked to a specific patient, to ensure patient confidentiality.

"We were able to determine moms HIV status by examining multiple pieces of evidence including diagnosis of HIV infection or AIDS, HIV/AIDS complications like pneumocystis pneumonia, a combination of complications and diagnoses or a record of AZT treatment," said Dr. Turner. "Similar criteria were used to determine the HIV status of children, but we looked for somewhat different HIV/AIDS complications that are characteristic of children and our criteria also differed by the childs age."

Researchers also used vital statistics records to gather additional information on factors like the mothers age, race, smoking history, and use of illicit drugs and alcohol.

Despite adjusting for these factors, smoking continued to have a strong association with an increased rate of maternal-fetal HIV transmission. This was especially true for women with later-stage AIDS.

AZT and other antiretroviral drugs were not widely used during the study years. Currently, pregnant women who are HIV-infected are being offered such drugs, which can reduce their viral load and the risk of transmission from approximately 1 out of 4 to approximately 1 out of 10.

"If a pregnant, HIV-positive woman takes AZT, or another antiretroviral drug, which reduces the mothers viral load, the effect of smoking on transmission may disappear, but smoking is still associated with low birthweight babies and poor birth outcomes for this very vulnerable population," said Dr. Turner.

Dr. Turner believes that this study underscores the need for healthcare providers to emphasize smoking cessation to all pregnant women, but especially those who are HIV-positive.

"Smoking is a difficult habit to beat, but it can be done," she said. "If healthcare providers use a number of different modalities to promote smoking cessation and employ vigorous follow-up of HIV-infected women, they can improve birth outcomes and may ultimately spare more children from contracting HIV."

This study was funded by the National Institute on Drug Abuse (NIDA), as part of its continuing effort to look at issues related to the healthcare delivery of HIV-infected drug using and non-drug using pregnant women and the impact of the delivery on birth outcomes (low birthweight and preterm birth) and HIV transmission.