There are few data about the influence of iron stores and anemia on pregnancy outcome. Results that are available are controversial. This study used the medical records of 202 pregnant women aged 29.5 + 4.8 years to examine the association of low and high ferritin levels and anemia with pregnancy outcome. Iron depletion (serum ferritin <20 µg/L) evaluated at 16 +/-4 weeks of gestation was present in 35% of subjects. Anemia affected 6.2%, 3.2%, and 24.2% of subjects during the first, second, and third trimesters. Average hemoglobin (Hb) measurements among anemic women were less than 110 g/L, less than 105 g/L, and less than 110 g/L in the first, second, and third trimesters, respectively. When hematocrit (Ht) values were used to diagnose anemia, the percentages of anemic women were 14.6% (Ht <0.33) in the first trimester, 22.6% (Ht <0.32) in the second trimester, and 39.8% (Ht <0.33) in the third tri-mester. Shorter gestation was found in women with a serum ferritin level below 20 µg/L (279 +/-1 d) or >50 µg/L (278 +/-2 d) than in women with intermediate levels (20 ug/L to 50 ug/L) (283 +/-1 d). When multiple regression analysis was used, an inverse relationship was also observed between first trimester anemia (low Ht levels) and birth weight and fetal growth ratio. No such association was observed during the second and third trimesters. The strength of this inverse relationship between first trimester Ht levels and birth weight and fetal growth ratio was similar to that between first trimester Ht levels and newborn sex and smoking, but much less than parity. This finding indicates the importance of evaluating iron status early in pregnancy.