Combination therapy which can suppress viral load
below the limit of detection (less than 500 copies) is likely to be advocated
even more strongly to pregnant HIV-positive women following the publication of
two studies which showed that not one woman with undetectable viral load passed
on HIV to her child. In comparison, one of the studies found that 63% of
untreated women with viral load above 100,000 copies gave birth to HIV-positive
babies.
Writing in the New England Journal of Medicine last
week, Patricia Garcia of Prentice Women's Hospital, Chicago, reported results
from the Women and Infants Transmission Study. This study measured viral load
and HIV transmission in 552 women offered AZT monotherapy during pregnancy
according to the ACTG 076 protocol (LINK to record).
In the same edition, Lynn Mofenson of the US National
Institute of Child Health and Development reported on the relationship between
viral load and transmission in PACTG 185, a study which investigated whether it
was beneficial to add hyperimmune globulin to AZT monotherapy during pregnancy
(no difference in transmission rates was found). Mofenson reported that none of
the mothers with undetectable viral load at the time of delivery transmitted HIV
to their infants.
On average, women who did not transmit HIV to their
infants had viral load in the region of 3,000 -4,000 copies, compared to an
average of 30,000 - 40,000 copies amongst women who did transmit HIV to their
infants. However, there was a significant difference in risk of transmission
between mothers with viral load below 500 copies and mothers with a low but
detectable viral load of less than 5,000 copies.
The Women and Infant Transmission Study found
substantial levels of HIV transmission even amongst women who would be
considered to have low viral load according to current HIV treatment
guidelines:
Mean viral load during pregnancy
Transmission rate on treatment
Transmission rate without treatment
<1,000
0%
0%
1,000 - 10,000
12%
20%
10,000 - 50,000
17.3%
24%
50,000 - 100,000
31 %
31%
>100,000
20%
63%
Reducing viral load to a low but detectable level did not always prevent HIV
transmission in those who received AZT during pregnancy. However, the study was
not able to distinguish whether other factors (such as mode of delivery, time
from rupture of membranes to birth, low birth weight, illicit drug use, smoking
or trial site) were associated with an increased risk of transmission in the
group with low but detectable viral load on treatment.
Other findings
Women who received zidovudine (AZT) were less likely to pass on HIV to theirbabies (note that both studies were carried out before the widespread
introduction of HAART)
No significant difference was found in viral load levels between mothers whotransmitted early in pregnancy and those who transmitted later on, or during
delivery. 72% of HIV-positive infants were believed to have been infected late
in pregnancy or during delivery in the Women and Infants Transmission
Study.
References
Garcia P et al. Maternal levels of plasma human immunodeficiency virus type 1
RNA and the risk of perinatal transmission. NEJM 341: 394-402, 1999.
Mofenson L et al. Risk factors for perinatal transmission of human
immunodeficiency virus type 1 in women treated with zidovudine. NEJM 341:
385-93, 1999.