Risk factors for in utero or intrapartum mother-to-child transmission in Thailand

The risk factors for mother-to-child transmission (MTCT) of HIV have been well documented: high maternal viral load, low CD4, sexually transmitted infections during pregnancy, prolonged ruptured membranes and vaginal delivery.

A paper authored by Gonzague Jourdain and coworkers, published in the December 1 2007 edition of Journal of Infectious Dieases, reported findings from an analysis of data from the Perinatal HIV Prevention Trial-1 (PHPT-1) from 24 June 1997 to 3 December 1999 performed to look at the role these factors play in relation to the timing of transmission.

PHPT-1 was a randomised, controlled, double-blind, two factorial trial of short (from 35 weeks gestation) versus long (from 28 weeks gestation) course AZT MTCT prophylaxis, conducted in 27 hospitals in Thailand. Infants received oral AZT for either three days or for 6 weeks (following the first interim analysis enrolment in the short-short arm was stopped). All infants were formula fed.

1437 antiretroviral-naive women were enrolled in the trail. Of 97 transmissions, 35 were in utero and 49 intrapartum.

In multivariate analysis, risk factors independently associated with in utero transmission were baseline maternal viral load of 35,000 copies/mL (AOR, 4.2) and delayed maternal AZT prophylaxis until >31.4 weeks gestation (AOR, 3.0).

Risk factors independently associated with intrapartum transmission were baseline HIV-1 load 10,000 copies/mL (AOR, 3.8 for 10,00035,000 copies/mL and 7.1 for 35,000 copies/mL), induction of labour, and premature labour (AOR, 2.6) with tocolysis (AOR, 15.1).

Risk factors independently associated with transmission overall were high baseline maternal viral load, high baseline maternal serum creatine level, premature labour with tocolysis, prematurity and low birth weight.

However, when the analysis was restricted to full-term infants, the association between low birth weight and transmission was not significant. The authors noted that only 10 women had creatinine levels 1.5 mg/dL so they were unable to investigate this observation further.

They wrote: To prevent in utero transmission, initiation of antiretroviral prophylaxis at 28 weeks gestation appears to be crucial. The fact that intrapartum transmission was found to occur at relatively low levels of maternal HIV-1 load suggests that minimising exposure to HIV and/or ensuring efficient pre-/postexposure antiretroviral prophylaxis is of paramount importance at the time of labour and delivery.

Jourdain G, Mary JY, Le Coeur S et al. Risk factors for in utero or intrapartum mother-to-child transmission of Human Immunodeficiency Virus Type 1 in Thailand. JID 2007:196. 1629.