Objective: The main objective of this prospective cohort study was to investigate the prevalence, risk factors and maternal-perinatal consequences of chronic asymptomatic intestinal parasitic infection during pregnancy. Methods: Prenatal patients ( n = 91) attending a public clinic in Quito, Ecuador, were followed during the third trimester. Intestinal parasite, nutritional status, sociodemographic/sanitation indicators and fetal outcome data were collected and analyzed using multivariate ANOVA and regression techniques. Results: Most subjects (93%) were infected with at least one species of pathogenic intestinal parasite: 88% with Entamoeba histolytica. Greater parasite burdens were associated with poorer maternal iron status and reduced fetal growth. In particular, a high E. histolytica load was associated with decreased maternal serum hemoglobin ( P = 0.002) and hematocrit levels ( P = 0.01), iron deficiency anemia ( P = 0.026), and indicators of diminished intrauterine growth including a decreased ponderal index ( P = 0.04), mid-arm circumference ( P = 0.01), and mid-arm/head circumference ratio ( P = 0.003). Conclusion: Asymptomatic intestinal parasitic infection represents a hidden risk factor for maternal iron deficiency anemia and fetal growth retardation.