By
Liz Highleyman
HIV
may be transmitted between infected women and their babies
during pregnancy, delivery, or breast-feeding. Yet studies continue to show
that taking a few precautions can reduce the risk of transmission to near zero.
Use
of zidovudine (AZT; Retrovir)
monotherapy and single-dose nevirapine (Viramune)
can dramatically lower the rate of mother-to-child transmission.
However, in developed countries, guidelines call for combination HAART, which
is more likely to fully suppress viral load and less likely to promote the emergence
of drug resistance.
Planned
Cesarean section before the start of labor can also play a role in reducing perinatal
transmission risk, though many experts believe this is not necessary if a woman
is on treatment and has a stable undetectable viral load in the third trimester.
In
developed countries were appropriate infant formula and sterile water are readily
available, HIV positive women are advised not to breast-feed. However, the World
Health Organization and UNAIDS acknowledge that exclusive breast-feeding may be
the best option in resource-limited settings.
As
reported in the May 11, 2008 issue of AIDS, researchers from the U.K. and
Ireland conducted a comprehensive national surveillance study of the impact of
different antiretroviral prophylaxis, delivery, and feeding strategies on prevention
of mother-to-child HIV transmission at the population level.
In
the U.K. and Ireland, pregnancies in HIV-infected women are reported to the National
Study of HIV in Pregnancy and Childhood; infant infection status is subsequently
reported. Factors associated with HIV transmission in this observational study
were analyzed for singleton births between 2000 and 2006.
Results
•
Routine screening
(introduced in Ireland in 1999 and the U.K. in 2000-2003) increased the proportion
of HIV positive women diagnosed before delivery from about 70% in 2000 to about
95% in 2005.
•
The overall
mother-to-child HIV transmission rate during the study period was 1.2% (61 out
of 5151 births).
•
This was a
decrease from around 20% in the mid-1990s (pre-HAART).
•
The transmission
rate fell to 0.8% (40 out of 4864 births) for women who received at least 14 days
of antiretroviral therapy, regardless of specific drug regimen or mode of delivery.
•
Transmission
rates for women following protocols recommended in the British HIV guidelines
were:
•
0.7% (17 out
of 2286 births) for HAART plus planned Caesarean section;
•
0.7% (4 out
of 559 births) for HAART plus planned vaginal delivery;
•
0% (0 out of
464 births) for zidovudine monotherapy plus planned Caesarean section (P = 0.150).
•
Longer duration
of HAART was associated with reduced transmission after adjusting for viral load,
mode of delivery, and infant sex (adjusted odds ratio 0.90 per week of HAART;
P = 0.007).
•
Among 2117
infants born to women on HAART with a viral load less than 50 copies/mL, only
3 (0.1%) were infected, 2 of whom had evidence of in utero transmission.
•
Of the 9 infected
children born to women with low or undetectable viral load, 4 had detectable virus
at birth, suggesting they were probably infected during gestation rather than
delivery.
Conclusion
Based
on the study findings, the investigators concluded that, "Sustained low HIV
transmission rates following different combinations of interventions in this large
unselected population are encouraging."
The
authors wrote that, "Current options for treatment and delivery offered to
pregnant women according to British guidelines appear to be effective," but
also noted that, "Although these guidelines recommend that most women should
receive HAART in pregnancy, zidovudine monotherapy with planned Caesarean section
remains an alternative for asymptomatic women with high CD4 cell count and low
viral load."
Current
U.S. guidelines for the prevention of perinatal HIV transmission are generally
similar to the U.K. recommendations. According to the latest U.S.
antiretroviral treatment guidelines, issued in December 2007, all HIV positive
pregnant women should receive combination antiretroviral therapy, regardless of
CD4 cell count. However, if a woman does not yet need treatment for her own health,
therapy may be deferred to the second trimester, since detrimental effects of
drugs on the fetus are most likely to occur during the earliest stages of development.
Since use of
prophylactic antiretroviral drugs in late pregnancy and during delivery has made
intra-partum mother-to-child HIV transmission rare, the study authors suggested
that in utero transmission during gestation -- possibly early in pregnancy --
is likely to account for an increasing proportion of perinatal infections. Starting
antiretroviral drugs sooner might reduce the transmission rate even further, but
they added that the benefits of earlier treatment "must be weighed against
concerns about drug toxicities and adverse pregnancy outcomes."
"Continuing
to improve the offer and uptake of antenatal HIV testing could have a significant
impact on further reducing [mother-to-child transmission]," said principal
author Claire Townsend of University College London, "since most perinatally
acquired infection is now in infants whose mothers are among the approximately
5% of infected women who remain undiagnosed at delivery."
MRC
Centre of Epidemiology for Child Health, Institute of Child Health, University
College London, London, UK; Guys & St Thomas' NHS Foundation Trust, London,
UK; Imperial College Healthcare NHS Trust, London, UK.
5/13/08
Reference
C
Townsend, M Cortina-Borja, C Peckham, and others. Low rates of mother-to-child
transmission of HIV following effective pregnancy interventions in the United
Kingdom and Ireland, 2000-2006. AIDS 22(8): 973-981. May 11, 2008.
Additional
Source
Kaiser Family Foundation. Appropriate Treatment Methods Can Prevent
Nearly All Risk of Mother-To-Child HIV Transmission, Study Says. HIV/AIDS Daily
Summary. May 7, 2008.
