Background: Anemia characterized by low hemoglobin concentration (HbC) is common in indoor housed pregnant sows. Iron is essential for hemoglobin synthesis and a number of metabolic processes including DNA synthesis and regulation of enzyme systems. In sows, anemia has been linked to lower HbC in piglets and increased occurrence of stillbirths. Therefore, the main objective of this study was to evaluate the effect of iron injection on hematology of pregnant sows and their offspring. Other objectives were to evaluate the effect of this injection on the probability of stillbirths and to study the tolerability of injected iron. Results: A sow herd with bi-weekly batch farrowing was selected for the study and 100 sows at mid-gestation were randomly assigned to either a treatment (FeT) or a control (FeC) group. At the time of recruitment to the study (baseline), 46% of the sows in the herd were anemic with a HbC less than 103 g/L. However, none of the anemic sows had iron deficiency anemia on erythrocyte characterization. HbC decreased numerically during gestation in both the FeT (- 2.48 g/L) and FeC (- 2.99 g/L) groups but the decrease was insignificant between the groups (P = 0.79). Likewise, the change from baseline to farrowing and from baseline to post-farrowing in other hematologic variables was similar for both groups. The percentage of transferrin saturation was not statistically different between groups (P = 0.14). There was a batch effect (week of breeding) in most of the hematologic variables. The probability of stillbirth in the two groups did not differ (P = 0.94). None of the hematologic variables in piglets was significantly different between the two groups. The sows tolerated the iron injection well. Conclusions: Intramuscular injection of two doses of 2500 mg iron 2 weeks apart at mid-gestation did neither change hematologic variables in sows nor in the piglets at farrowing. Similarly, iron treatment did not reduce the probability of stillbirths among the offspring. The sows recruited in this study tolerated the iron injections well. Further characterization of erythrocytes did not support that sows had iron deficiency anemia at baseline. Therefore, further studies on animals with well-defined anemia and with focus on the iron regulating hormone hepcidin are recommended.