Maternal undernutrition is critical in the etiology of poor perinatal outcomes and accounts for 20% of small-for-gestational-age (SGA) births. High levels of food insecurity, antenatal undernourishment, and childhood undernutrition necessitate the supplementation of fortified balanced energy protein (BEP) during pregnancy in low-income settings especially with scarce literature available in the subject. Hence, this paper extensively covers the protocol of such a trial conducted in an urban slum of Karachi, Pakistan. The trial is community-based, open-labelled, four-arm, and randomized controlled that will include parallel group assignments with a 1:1:1:1 allocation ratio in low-income squatter settlements in urban Karachi, Pakistan. All pregnant women if identified between >8 and <19 weeks of gestation based on ultrasound, will be offered routine antenatal care (ANC) counseling and randomly allocated to one of the four arms receiving: (1) ANC counseling only (control group), (2) ANC counseling plus BEP supplement (intervention arm 1), (3) ANC counseling plus BEP supplement plus 2 doses azithromycin (intervention arm 2), or (4) ANC counseling plus BEP supplement plus daily dose of nicotinamide and choline (intervention arm 3).