An open-label, single arm, multicentre study to determine the virologic and immunologic responsiveness of women, who previously received a regimen of nevirapine for the prevention of MTCT, to a regimen of nevirapine and ZDV+3TC treatment. As well as to evaluate the proportion of patients who fail this treatment at 24 and 48 weeks, and to evaluate the resistance profile of HIV isolates from patients who fail nevirapine and ZDV+3TC treatment.