Low dose iron supplementation does not cover the need for iron during pregnancy

Abstract

Objective: To determine: 1) if 18 mg iron daily is sufficient to cover the iron need during normal pregnancy, and 2) if women, who will not need iron supplementation during pregnancy, can be identified by early screening.

Design: In a prospective study the women were randomized to receive either 18 or 100 mg iron daily from the 16th week until delivery. Investigations were performed in the 16th, 30th, and 38th week.

Subjects: Healthy nulliparae (n = 43) experiencing a normal singleton pregnancy. Only women with a normal hemoglobin concentration and intact iron stores (S-Ferritin > 15 micrograms/1) in the 16th week were included.

Variables: These measurements were done consecutively: 1) the total hemoglobin mass (with carbon monoxide). 2) S-Ferritin, 3) S-Transferrin, 4) S-Iron, 5) red cell indices (hemoglobin concentration, hematocrit, MCV, MCHC).

Results: Changes in red cell indices and S-Transferrin were equal in the two groups. There was no significant difference in S-Ferritin in the 16th week. In the 30th week 3 women (14%) in the 100 mg group and 11 (52%) in the 18 mg group had empty iron stores (p < 0.05). The numbers were 1 (5%) and 15 (72%) in the 38th week (p < 0.0001). The increment in total hemoglobin mass was equal in the two groups from the 16th to the 30th week (13% in the 100 mg group and 12% in the 18 mg group). From the 30th to the 38th week the increment in total hemoglobin mass was largest in the 100 mg group (8.1% versus 2.7%, p < 0.05).

Conclusion: Despite a normal hemoglobin concentration and intact iron stores in the 16th week, an iron supplementation of 18 mg daily is not sufficient to cover the iron need in many pregnant women in the 3rd trimester.