In a national surveillance study of singleton births to HIV-infected women in the United Kingdom and Ireland, the rate of mother-to-child HIV transmission was 1.2% overall, and 0.8% for women who had received antiretroviral therapy for at least the last 14 days of pregnancy. Transmission rates were 0.7% for women who had received highly active antiretroviral therapy (HAART) and had either a planned cesarean section or a planned vaginal delivery, and 0.0% for those who had received zidovudine monotherapy and had a planned cesarean delivery. After adjustment for maternal HIV viral load, delivery mode and infant’s sex, each additional week of HAART was associated with a reduced risk of HIV transmission (odds ratio, 0.9).
Because HAART, appropriate management of delivery and avoidance of breast-feeding have virtually eliminated mother-to-child HIV transmission in resource-rich countries, researchers explored the influence of different treatments in the United Kingdom and Ireland, where 95% of infected women are identified before delivery. In a population-based study, using data on all reported pediatric and obstetric HIV infections, researchers examined mother-to-child transmission rates for women who had singleton births between 2000 and 2006. They considered only antepartum treatment, divided into four categories: none, zidovudine monotherapy, dual therapy and HAART. The analysis used logistic regression to assess characteristics associated with the risk of mother-to-child transmission.
Among the 5,930 infants included in the study, a large majority were born to black African women (79%) and to women who were asymptomatic (90%). Eighty-two percent of women had received HAART, 12% zidovudine monotherapy, 2% dual therapy and 3% no therapy. Fifty-seven percent had had an elective cesarean section, 21% an emergency cesarean and 22% a vaginal delivery. One-fourth of women receiving HAART had started it prior to getting pregnant, and among those who had begun treatment during pregnancy, the median gestational age at initiation was about 26 weeks; the median gestational age at initiation of monotherapy was 28 weeks. More than half of women on HAART had an undetectable viral load at about the time of delivery; for those on monotherapy, the median viral load was detectable but low.
The overall mother-to-child transmission rate was 1.2%, and the rate for women who had received any antiretroviral therapy for at least the last two weeks of pregnancy was 0.8%, regardless of delivery mode. The transmission rate was 0.7% for women who had received HAART and had either a planned cesarean section or a planned vaginal delivery, and 0.0% for those treated with zidovudine monotherapy who had a planned cesarean; among untreated women, the transmission rate was 9%.
In multivariable analysis of 4,892 births that controlled for therapy type, delivery mode, gestational age and sex of infant, women who had received no treatment had an increased risk of mother-to-child transmission compared with those who had received HAART, and women who had given birth to girls rather than boys also had an elevated risk of transmission (odds ratios, 9.1 and 1.9, respectively). Compared with a gestational age of 37 weeks or more, a gestational age of less than 32 weeks was another significant risk factor for transmission (3.6); however, the women in all seven of these cases had received no treatment or less than three weeks of therapy, and all but one had delivered vaginally.
When multivariable analysis was further restricted to the 4,084 births for which maternal viral load was reported and controlled for, higher viral load was associated with an increased risk of transmission (odds ratio, 2.4). This model also found that women who had received no treatment were at greater risk than those who had received HAART, as were women who had had a vaginal delivery instead of a planned cesarean section (3.2 and 2.4, respectively). In an analysis that adjusted for viral load, delivery mode and infant’s sex, women who had begun HAART during pregnancy had a decreased risk of transmission with each additional week of treatment that they received (0.9).
The researchers believe that their findings support the British national guidelines for HIV treatment of pregnant women, under which HAART is the recommended regimen for most women, and zidovudine monotherapy with an elective cesarean section is recommended for those with high CD4 cell counts and low viral loads. They suggest that a possible weakness of their study is that the HIV infection status was unavailable for 13% of infants; because these children’s mothers are more likely than the others to have recognized risk factors for mother-to-child transmission, the overall transmission rate may be slightly underestimated.
Given the success of antiretroviral therapy in reducing the rate of mother-to-child transmission of HIV, the researchers recommend that Ireland and the United Kingdom continue to promote early antenatal HIV testing. Furthermore, they assert that “these population data provide important evidence to support the targeted use of different combinations of interventions for preventing [mother-to-child transmission].”
1. Townsend CL et al., Low rates of mother-to-child transmission of HIV following effective pregnancy interventions in the United Kingdom and Ireland, 2000–2006, AIDS, 2008, 22(8):973–981.