An elective caesarean delivery, even when a woman has an undetectable viral load, significantly reduces the risk of mother-to-baby transmission of HIV, according to a study published in the February 1st edition of Clinical Infectious Diseases.
In countries with widespread access to HAART, preventative interventions including the use of HAART during pregnancy and elective caesarean delivery mean that there is a very low rate of mother-to-baby transmission of HIV. The ability of HAART to reduce maternal viral load, if used appropriately during pregnancy, has led some clinicians to question the added benefit of elective caesarean delivery if a mother has an undetectable viral load.
Even with the use of interventions to prevent vertical transmission of HIV, a small number of infants continue to be infected with HIV by their mother during pregnancy or delivery. Investigators from the European Collaborative Study wished to investigate the effects of elective caesarean delivery, duration of membrane rupture, and prematurity on the risk of mother-to-baby HIV transmission.
Characterists of the European Collaborative Study population
Data from 183 mother-child pairs enrolled from 1997 (when the use of HAART first became widespread) until May 2004 were included in the investigators’ analysis. The majority of women (70%) were infected with HIV through heterosexual sex, two-thirds knew that they were HIV-positive before pregnancy, and 90% had a CD4 cell count above 200 cells/mm3.
The percentage of women having an elective caesarean delivery increased from approximately 40% in 1997 to 70% in 1999, before falling to approximately 60% in 2002, followed by an increase to 70% in 2003.
A total of 1147 women received HAART during pregnancy, 57% of these women taking HAART for the first time during pregnancy. The proportion of women who received HAART before pregnancy increased significantly from 5% in 1997, to 83% in 2000 to 85% in 2003.
Mother-to-baby transmission rates
The overall mother-to-baby transmission rate was a little under 3%, but this varied over time, falling from 5% in 1997-98 to just under 1% in 2001-02. Use of antiretroviral medication was significantly associated with a reduced risk of mother-to-baby transmission, the rate being 11.5% for women who did not take HAART versus 1% for women who took HAART (p
Amongst women who received HAART, the risk of mother-to-baby transmission was lower for those women who had started HAART before pregnancy (0.25% transmission rate) compared to the risk for women who started HAART during pregnancy (1% transmission rate, p = 0 .02).
Transmission and mode of delivery
Mode of delivery was associated with transmission. Of the 369 infants delivered vaginally, 24 (7%) were infected with HIV, compared to six of the 239 (3%) infants delivered by emergency caesarean section, and 16 of the 971 (2%) of the babies delivered by elective caesarean (p
Rupture of the membranes
Details of maternal membrane rupture were available for 204 of the vaginally delivered babies. The median duration of membrane rupture (4.5 hours) was significantly higher for infected infants compared to uninfected infants (1.5 hours, p
Of the 207 infants born by caesarean delivery for whom details on maternal membrane rupture were available, 50 were born with intact membranes and no cases of HIV transmission. Seven of the remaining infants were HIV infected, median duration of rupture being five hours.
Risk factors for mother-to-baby transmission
Viral load was identified as the principal risk factor for mother-to-baby transmission of HIV in the HAART era. A maternal viral load above 1,000 copies/ml was associated with a twelve-fold increase in the risk of HIV transmission (p = 0.002). Elective caesarean delivery reduced by two-thirds the risk of HIV transmission compared to vaginal delivery(p = 0.04).
Elective caesarean delivery, undetectable viral load and/or HAART
Among the 560 women with an undetectable viral load, elective caesarean delivery was associated with a significantly reduced rate of mother-to-child transmission compared to either emergency caesarean or vaginal delivery (p = 0.004).
In further analysis, which only included the mother-child pairs receiving antenatal HAART, elective caesarean delivery was associated with a 40% reduction in the risk of mother-to-child transmission compared with vaginal delivery.
Infection despite maternal HAART
In total, eleven infants were infected with HIV even though their mothers received HAART. However, only one of these women had been taking HAART before her pregnancy, and the median duration of HAART in the other ten women before delivery was only 38 days. The eleven women also had relatively advanced HIV disease, the median CD4 cell count being 209 cells/mm3. Only five of the infants were born using elective caesarean delivery.
“A high maternal viral load was the key risk factor for mother-to-child transmission of HIV, and the only other factor achieving statistical significance…in the HAART era was elective caesarean section delivery”, write the investigators.
The investigators add, “even in the HAART era, we were able to show a significant reduction (two-thirds) in the risk of mother-to-child transmission of HIV associated with elective caesarean section delivery”.
HIV in the genital tract compartment of women with an undetectable plasma viral load could explain why a small number of infants were infected with HIV by mothers with an undetectable viral load.
Although it has been optimistically suggested that it would be possible to eliminate mother-to-baby transmission of HIV in countries with ready access to HAART, the investigators note that they have shown that a small number of vertical infections still occur. This is likely to be between 1%-2%, but the use of elective caesarean could reduce this further to 0.5%-1%.
“On an individual level”, conclude the investigators, “the decision regarding mode of delivery rests with the woman and her clinician, who should inform her of the potential risks and benefits.”
European Collaborative Study. Mother to child transmission of HIV infection in the era of highly active antiretroviral therapy. Clin Infect Dis 40: 458 – 465, 2005.