Background : Evidence has shown that maternal HIV infection has adverse effect on pregnancy outcomes including childbirth weight and that knowledge of mothers HIV status affects practice of exclusive breastfeeding for the first six month. Using methods for matching possible confounders, the purpose of this study were twofold: a) to assess whether or not the association of maternal HIV on childbirth weight was moderated by use of ART drugs and b) to determine if indeed knowledge of HIV status among mothers was associated with exclusive breastfeeding. Methods: Data on over 18,000 and 16,000 children still alive and born within five years of the 2010 and 2015-16 Malawi Demographic and Health Surveys (MDHS) were analysed. A set of methods for confounder balance namely, the 1:1 nearest neighbour (NN) matching, matching on the propensity score (PS) and inverse weighting the propensity score (PS) were used. Results: Using the 2010 data, maternal HIV infection had a negative effect on infant birth weight -149.0 (-324.2, -26.2) and -154.3 (-295.4, -13.3), under PS matching and PS inverse weighting respectively. Infant birth weights from HIV-infected mothers on ART and uninfected mothers were the same (mean: 3121.3, 95% CI: 3021.9, 3220.7) and (3273.7, 95% CI: 3259.1, 3288.3), respectively) and differed significantly from those HIV-infected mothers (3193.9, 95% CI: 3122.2, 3265.6). For the 2015-16 data, mothers who were HIV-infected gave birth to infants who significantly weighted more than infants from HIV-uninfected mothers 144.7 (40.4, 249.1) and 115.4 (11.6, 219.2), under PS matching and PS inverse weighting respectively. Knowledge of HIV status among mothers was not associated with their behaviour concerning exclusive breastfeeding for the 2010 and 2015-16 data. Conclusion: The association between maternal HIV infection and birth weight depended on the data used, with the 2010 data showing adverse effect. The higher birth weight among infants born to HIV infected mothers in 2015-16 maybe indicative of successes of policies and interventions within the PMTCT program in Malawi. The observed mitigating effect of ART usage by HIV infected mothers on child birth weight further confirms that PMTCT interventions should continue to be supported among antenatal clinics in Malawi.