Improving maternal nutrition practices during pregnancy is essential to save lives and improve health outcomes for both mothers and babies. This paper examines the maternal, household, and health service factors influencing maternal nutrition practices in the context of a large scale maternal, newborn, and child health (MNCH) program in Bangladesh. Data were from a household survey of pregnant (n = 600) and recently delivered women (n = 2,000). Multivariate linear and logistic regression analyses were used to examine the determinants of three outcomes: consumption of iron and folic acid (IFA) tablets, calcium tablets, and diverse diets. Women consumed 94 ± 68 IFA and 82 ± 66 calcium tablets (out of 180 as recommended) during pregnancy, and only half of them consumed an adequately diverse diet. Good nutrition knowledge was the key maternal factor associated with higher consumption of IFA (β = 32.5, 95% CI: 19.5, 45.6) and calcium tablets (β ~31.9, 95% CI: 20.9, 43.0) and diverse diet (OR = 1.8, 95% CI: 1.0–3.1), compared to poor knowledge. Women’s self-efficacy in achieving the recommended practices and perception of enabling social norms were significantly associated with dietary diversity. At the household level, women who reported a high level of husband’s support were more likely to consume IFA (β = 25.0, 95% CI: 18.0, 32.1) and calcium (β = 26.6, 95% CI: 19.4, 33.7) tablets and diverse diet (OR = 1.9, 95% CI: 1.2, 3.3), compared to those who received low support. Health service factors associated with higher intakes of IFA and calcium tablets were early and more prenatal care visits and receipt of free supplements. Combined exposure to several of these factors was attributed to the consumption of an additional 46 IFA and 53 calcium tablets and 17% higher proportions of women consuming diverse diets. Our study shows that improving knowledge, self-efficacy and perceptions of social norms among pregnant women, and increasing husbands’ support, early registration in prenatal care, and provision of free supplements will largely improve maternal nutrition practices.