We used data from a large clinical trial, the Breastfeeding, Antiretrovirals and Nutrition (BAN) Study (www.thebanstudy.org), and a nutrition sub-study of BAN, the Malawi Mothers and Infants (MaMi) Study. The BAN study was a large clinical trial that aimed to promote maternal and infant health in HIV-infected Malawian women and their infants, and to prevent maternal to child transmission of HIV by providing a lipid based nutrient supplement (LNS) to the mother and antiretroviral drugs to the mother or infant. Mother-infant pairs (n=2,369) were randomized using a two-arm nutritional and three-arm drug to six study arms: maternal LNS/maternal ARV (mLNS-mARV), maternal LNS/infant ARV (mLNS-iARV), maternal LNS (mLNS), maternal ARV (mARV), infant ARV (iARV), or control (C). The data used in this analysis was derived from screening visits and numerous visits from birth to 24 weeks postpartum. This study provided a novel opportunity to understand how maternal nutritional status was related to infant status, and how infant status related to maternal status. We chose to examine two important aspects of maternal and infant nutritional status during this time: iron and anthropometry. We observed that among mothers with low body mass index (BMI) maternal weight loss was related to less infant weight and length gain from birth to six months in girls. In longitudinal models, higher maternal Hb was associated with higher concurrently measured infant Hb, especially between 6 and 18 wk. In the MaMi substudy, we observed that increases in maternal TfR and Hb were associated with an increase in infant Hb and TfR from initial measurement to 24 weeks. These findings suggest that maternal breastmilk quality may be compromised in thin women who lose weight, adversely affecting infant growth in females. The observed maternal influence in iron models suggests optimizing maternal iron status during pregnancy and lactation is important for reducing risk of infant iron depletion. Together these results highlight that promoting maternal nutritional status benefits not only the mother, but her infant as well.