For 227 women participating in a zinc supplementation trial in Lima, Peru, we used multiple regression techniques to identify maternal socioeconomic, health and nutritional factors influencing hemoglobin (HB) concentrations at baseline, when women entered prenatal care between 1024 wks gestation. HB concentrations (g/L) declined with increasing wks of gestation, from 118.2 ± 18.2 at 10 wks, to 110.3 ± 14.6 at 18 wks, to 102.1 ± 14.6 at 24 wks gestation. After adjusting for duration of pregnancy, variation in HB concentration was associated negatively with maternal parity (P < 0.05). Body mass index (BMI), mid-upper arm circumference (MUAC), triceps and sub-scapular skinfold thickness measures were each positively associated with, and equally predictive of, HB levels, whereas calf circumference and calf skinfold thickness were not important factors. The results suggest that maternal health and nutritional factors are related to HB concentrations, and in particular, highlight the potential importance of upper body size and fat stores in influencing HB concentrations during pregnancy.