A prospective observational study was performed on 488 women with haemoglobin >/=10 g/dl at booking to examine the relationship between serum ferritin concentration quartiles at 28-30 weeks gestation with maternal characteristics, pregnancy complications and infant outcome. While there was no difference in the maternal characteristics or gestational age, the infant size decreased significantly and progressively from the lowest to the highest quartile. Despite a significant difference in the incidence of multiparous women, there was no difference in the incidence of most complications except for prelabour rupture of the membranes and infant admission to the neonatal unit. Compared with the other three quartiles, the highest quartile was associated with increased risk for preterm delivery and neonatal asphyxia, while the lowest quartile was associated with decreased risk of pre-eclampsia, prelabour rupture of the membranes, and infant admission to the neonatal unit. Overall, ferritin quartiles were correlated with other parameters of iron status and red cell indices, and ferritin concentration was inversely correlated with infant birthweight. Our findings suggested that maternal ferritin concentration is primarily a reflection of maternal iron status, and a high level is associated with unfavourable outcome. The rationale of routine iron supplementation in non-anaemic women needs to be re-examined.