Guidelines for the management of HIV infection in pregnant women and the prevention of mother-to-child transmission

The risk of transmission is related to maternal health, obstetric factors and infant prematurity. Overall there is a close linear correlation between maternal viral load and risk of transmission, but as yet the evidence for a threshold below which transmission never occurs is limited [4]. This may be due to discrepancies between plasma and genital tract viral loads. However, the major studies of viral load and transmission have used assays with a lower limit of detection of 500-1000 HIV RNA copies/mL, and a relative insensitivity for some non-B subtypes. CD4 lymphocyte counts and clinical disease stage have been shown in some cohorts to have an association with the risk of transmission even after controlling for viral load [5]. The only obstetric factors that consistently show an association with risk of transmission are mode of delivery and duration of membrane rupture but invasive procedures in labour are generally avoided as they pose a theoretical risk of iatrogenic transmission. Delivery before 34 weeks of gestation has been shown to be associated with an increased risk of transmission [6]. Formula feeding has been advocated for positive women since the association with breast feeding and increased transmission was noted in 1992 [7]. The protective role of caesarean section has been clarified with both a meta-analysis [8] and a RCT reported in 1999 [9]. The findings of the first RCT, published in 1994, showing that monotherapy with zidovudine (ZDV) could reduce transmission from 25% to 8% in a non-breast feeding population [10], have been supported by numerous observational studies confirming this reduction in clinical practice. Subsequent studies have shown equivalent benefit in mothers with more advanced disease and in those who are more heavily pretreated. As standard treatment for nonpregnant adults is now with at least three antiretrovirals more women are taking combination therapy in pregnancy [2]. There are still relatively few data, however, on the safety of antiretroviral therapy (ART) in pregnancy and the management of any HIV-positive pregnant woman requires a careful consideration of the balance between the mother's own health needs, the need to reduce vertical transmission and possible adverse effects of ART to the fetus.