Worldwide, between one-fourth and one-third of infants born to women infected with HIV become infected themselves. Promoting HIV prevention among women is the primary means of preventing HIV infections among infants. For those women who do become infected, preventing pregnancy is a secondary way of reducing the spread of HIV to infants. For HIV-infected women who become pregnant, transmission to infants can occur in utero, during birth or through breastfeeding.
Between one-fourth and one-third of infants born to women infected with HIV worldwide become infected themselves.1 Called "vertical" or "perinatal" transmission, passing this infection from mother to child is the primary means by which infants acquire HIV.
Most pregnant women with HIV have been infected through unprotected intercourse. Consequently, providers should recognize that promoting HIV prevention among women is the primary means of preventing HIV infections among infants. For those women who do become infected, preventing pregnancy is a secondary way of reducing the spread of HIV to infants.
Although it is clear that infections can occur in utero, during birth or through breastmilk, researchers are not sure about the relative risk associated with each phase.
"In the future, new research findings may affect recommendations to help HIV infected pregnant women protect their offspring from HIV," says Elizabeth Preble of FHI's AIDS Control and Prevention (AIDSCAP) Project. "In the meantime, however, policy-makers should understand that our current knowledge about HIV transmission to infants involves complex issues such as breastfeeding versus bottlefeeding, voluntary and available HIV testing, and other issues." Preble is drafting guidelines for the World Health Organization (WHO) on STD prevention in the maternal and child health/family planning setting.
Pregnancy and delivery
During pregnancy, the stage of maternal infection can affect perinatal transmission rates. The greater the progression of disease in the mother, as measured by viral load or CD4 cell counts, the more likely is transmission. Other factors that may increase the risk include hemorrhage during labor, vaginal delivery, duration of labor after the rupture of membranes, and some obstetrical approaches. Amniocentesis or other invasive procedures before labor are also factors that may increase the risk.2
In 1994, a clinical trial showed that drug therapy with zidovudine, or AZT, decreased transmission from pregnant mother to newborn. AZT was given to women after their first trimester of pregnancy, intravenously during labor and delivery, and was given to their infants for the first six weeks of their lives.3 In countries where AZT is available, AZT therapy increased dramatically after the report.
In a follow-up study of 103 infants whose infected mothers received AZT therapy and 453 infants whose mothers did not, HIV transmission was 19 percent among those not using AZT but only 8 percent among those receiving therapy.4
Currently, the cost of drugs such as AZT is prohibitively expensive in most developing countries. Studies are testing new drugs and simpler regimens that may curtail transmission at lower cost.
(In January, a U.S. National Institutes of Health advisory panel recommended that infected mothers should continue taking AZT to reduce chances of infecting their babies, despite a National Cancer Institute study that raises questions about whether the drug may increase cancer risks. The study found high doses of AZT increased lung, liver and skin cancers in baby mice. However, there is no evidence of any human child getting cancer after AZT treatment, and a study by the manufacturer of AZT found no risk among mice from lower doses that would be equivalent to those given pregnant women.)
Other research is testing treatments with a specially made immunoglobulin, which contains antibodies to HIV. This immunoglobulin comes from infected individuals, but it has been carefully treated to kill HIV and other infectious agents. It theoretically should boost the immune systems of pregnant mothers and infants, so that the virus is less likely to be transmitted from mother to child.
Some studies have suggested that cesarean section delivery in HIV-infected mothers can have a protective effect by avoiding passage through the birth canal, where there is contact with infected maternal blood and cervical fluids. However, study results are inconclusive.
Moreover, cesarean births, especially in developing countries, have a relatively high risk of postoperative mortality. Two recent studies provide some evidence that complications of a cesarean section are common among HIV-positive women, particularly those who have severely suppressed immune systems.5
Obstetrical interventions that could increase the risk of HIV transmission should be avoided. The rupture of membranes for more than four hours prior to delivery may be associated with increased risk of HIV infection, so intentionally rupturing the membranes to induce or accelerate labor should be avoided.6 Also, placing internal fetal-scalp electrodes should be avoided when labor can be managed safely with external fetal monitoring.7
Other types of interventions under consideration are disinfecting the birth canal of HIV-infected women and using vitamin A. A recent study using chlorhexidine to wash the birth canals of HIV-infected women in Malawi did not reduce the transmission rate except among those whose membranes were ruptured more than four hours before delivery.8 Another Malawi study suggested that maternal vitamin A deficiency contributed to the risk of perinatal transmission.9 Studies are testing a vitamin A supplementation program, which would be practical and inexpensive in resource-poor settings.
Breastfeeding
The benefits of breastfeeding are well established. It promotes development of a newborn's gastrointestinal and immune systems and, by enhancing immunity, lowers the risk of diseases such as meningitis and infections of the respiratory system. Breastfeeding protects babies from diarrhea, the major cause of infant death in developing countries, and provides excellent nutrition without potential infection from unclean water. It also benefits the mother, including a more rapid postpartum recovery and a reduction in breast cancer risk. Finally, breastfeeding is a key component of the lactational amenorrhea method (LAM) of pregnancy prevention.
However, studies have shown conclusively that breastmilk transmits HIV. A review of four studies of women who acquired HIV infection postnatally estimated the risk of transmission through breastfeeding at 29 percent. The same review analyzed five studies in which the mother was infected prenatally and found an additional risk of transmission through breastfeeding, over and above transmission in utero or during delivery, to be 14 percent.10
Several models have sought to determine whether a change from breastfeeding to bottlefeeding would result, on balance, in a higher or lower child mortality. The models weighed the risk of HIV infection against the risk of dying from diarrhea and other infections.11
The models suggest different breastfeeding policies for three different settings. Most models conclude that for places where infant mortality, HIV prevalence and mortality from bottlefeeding are all high, any change from breastfeeding to bottlefeeding would harm a child's prospects for survival.
In affluent, industrialized countries, where bottlefeeding has little adverse effect on child mortality, bottlefeeding by known HIV-infected mothers can increase child survival.
In intermediate settings, the appropriate policy is not clear. In 1992, WHO and the United Nations Children's Fund (UNICEF) considered relative risks carefully in making recommendations for these intermediate settings. Where other infectious diseases and malnutrition are primary causes of infant deaths, the recommendations say, "breastfeeding should remain the standard advice to pregnant women, including those who are known to be HIV-infected, because their baby's risk of becoming infected through breastmilk is likely to be lower than its risk of dying of other causes if deprived of breastfeeding."12
Few developing countries are prepared to provide universal HIV testing for pregnant women. One exception is Thailand, where such testing occurs in some areas. "Women identified as HIV-infected in early pregnancy are advised to seek a termination, those identified in later pregnancy are told to bottlefeed and given supplies of breastmilk substitutes," report Dr. Angus Nicoll of the Communicable Disease Surveillance Centre in London and colleagues.13 Voluntary HIV counseling and testing can give pregnant women the information they need to make an informed decision about their current pregnancy and future childbearing.
-- William R. Finger
References
Joint United Nations Programme on HIV/AIDS (UNAIDS). HIV and infant feeding: An interim statement. Wkly Epidemiol Record 1996;71:289-91.
Sperling RS, Shapiro DE, Coombs RW, et al. Maternal viral load, zidovudine treatment, and the risk of transmission of human immunodeficiency virus type 1 from mother to infant. N Engl J Med 1996;335(22):1621-29; Mandelbrot L, Mayaux M-J, Bongain A, et al. Obstetric factors and mother-to-child transmission of human immunodeficiency virus type 1: The French perinatal cohorts. Am J Obstet Gynecol 1996;175(3):661-7; Landesman SH, Kalish LA, Burns DN, et al. Obstetrical factors and the transmission of human immunodeficiency virus type 1 from mother to child. N Engl J Med 1996;334(25):1617-23; St. Louis ME, Kamenga M, Brown C, et al. Risk for perinatal HIV-1 transmission according to maternal immunologic, virologic, and placental factors. JAMA 1993;269(22):2853-59.
Zidovudine for the prevention of HIV transmission from mother to infant. MMWR 1994;43:285-7.
Cooper ER, Nugent RP, Diaz C, et al. After AIDS clinical trial 076: The changing pattern of zidovudine use during pregnancy, and the subsequent reduction in the vertical transmission of human immunodeficiency virus in a cohort of infected women and their infants. J Infect Dis 1996;174:1207-11.
Bulterys M, Chao A, Dushimimana A, et al. Fatal complications after Cesarian section in HIV-infected women. AIDS 1996; 10(8):923-4; Semprini AE, Castagna C, Ravizza M, et al. The incidence of complications after caesarean section in 156 HIV-positive women. AIDS 1995;9(8):913-7.
Landesman.
Landers D, Sweet R. Reducing mother-to-infant transmission of HIV -- the door remains open. N Engl J Med 1996;334(25):1664-5.
Biggar RJ, Miotti PG, Taha TE, et al. Perinatal intervention trial in Africa: Effect of a birth canal cleansing intervention to prevent HIV transmission. Lancet 1996; 347:1647-50.
Semba RD, Miotti PG, Chiphangwi JD, et al. Maternal vitamin A deficiency and mother-to-child transmission of HIV-1. Lancet 1994;343:1593-7
Dunn DT, Newell ML, Ades AE, et al. Risk of human immunodeficiency virus type 1 transmission through breastfeeding. Lancet 1992;340:585-8.
Nicoll A, Newell M-L, Van Praag E, et al. Editorial review: Infant feeding policy and practice in the presence of HIV-1 infection. AIDS 1995;9:107-19; Kennedy KI, Fortney JA, Bonhomme MG, et al. Do the benefits of breastfeeding outweigh the risk of potential transmission of HIV via breastmilk? Trop Doct 1990;20:25-29.
Consensus Statement from the WHO/UNICEF Consultation on HIV Transmission and Breastfeeding, Geneva 30 April-1 May, 1992.
Nicoll.
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