Difference in placental parasitaemia between HIV seropositive and HIV seronegative women was used to determine sample size. Using a power of 90% and a significance level of 5%, the sample size needed to detect a true difference in prevalence of maternal placental parasitaemia in the two study groups will be 104 women per group. However, to compensate for loss of follow-up, 30% will be added per group and this will give a total of 135 HIV seropositive women in each arm, giving a total of 270 HIV sero-positive mothers in the two study arms. Since HIV sero-prevalence in primigravidae attending antenatal care in the district is 10%, a minimum number of 1274 women would be required in each arm (total 2548).