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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