Higher risk of transmission with delayed control of maternal viral load despite viral loads of <500 copies/mL at delivery
Polly Clayden. HIV i-Base
A poster from the French Perinatal Cohort showed results from a case control study looking at transmission among women receiving ART with viral load <500 copies/mL at delivery.
Between 1997 and 2006 the reported MTCT rate in this cohort was 1.6% and 0.6% for those with viral load <500 copies/mL at delivery.
In this case note review, the investigators matched 3 to 4 uninfected infants with each infected child from a total of 3972 infants. They included 19 cases and 60 controls and the women were well matched for origin, first appointment, timing of HIV diagnosis, timing of last viral load test, type of ART and mode of delivery.
Of the infected infants (n=16) 39% had positive PCR at birth, indicating infection in utero. There was a higher proportion of women with viral load >1000 copies/mL in cases than controls at 28 weeks, 92.3% vs 31%, p=0.03 and 32 weeks, 78.6% vs 26.3%, p=0.04. And when the investigators restricted the analysis to intrapartum transmission the results remained statistically significant, 100% vs 25%, p<0.01 at 28 weeks and 85.7% vs 23.5%, p<0.01 at 32 weeks.
Women in the control group were more likely to have initiated ART before they became pregnant than the cases, 45% vs 16%, p=0.02. Among the 49 mothers initiating ART in pregnancy, viral load decrease was slower among cases vs controls despite similar timing of initiation, 29.5 weeks (IQR 23 to 31.5) in cases vs 30 weeks (IQR 24-32) in controls.
The investigators wrote: Insufficient control of viral load (>1000 copies/mL) at 28 to 32 gestational weeks is a risk factor of residual HIV-1 MTCT even in mothers under ART with a controlled viral load near delivery. This concerns intra-partum as well as in utero transmission.
This study underscores the importance of controlling viral load in the third trimester and not only at delivery.
Tubiana R et al. Delayed control of maternal viral load during pregnancy is associated with higher risk of MTCT despite viral loads of <500 copies/mL at delivery: A case/control study in the ANRS French Perinatal Cohort CO1/10/11. 16th CROI, Montreal, 2009. Abstract 929.