Gestational diabetes mellitus in the last trimester - a feature of maternal iron excess?

Aim To determine whether non-anaemic women with gestational diabetes mellitus (GDM) diagnosed in third trimester pregnancy have evidence of increased iron stores compared with matched non-diabetic controls. Methods In a prospective study, women who had antenatal booking before 20 weeks' gestation and without anaemia or diabetes mellitus were recruited at the time of the oral glucose tolerance test (OGTT) at 28-31 weeks' gestation for the study of serum ferritin, iron and transferrin concentrations. The results were blinded to the managing obstetricians. After delivery, the records were reviewed. The cases diagnosed as GDM were compared with a control group (two controls for each index case matched for parity) selected at random from the at-risk but nondiabetic cases. Results GDM was diagnosed in 97 of the 401 women recruited. Compared with the 194 controls, there was no difference in the weight, body mass index, booking and third trimester haemoglobin, or third trimester red cell indices, but concentrations of serum ferritin, iron, transferrin saturation, and the post-natal haemoglobin were significantly higher. On multiple regression analysis, maternal BMI and the log-transformed ferritin concentration remained significant determinants of the OGTT 2-h glucose value. Conclusion The results suggest an association between increased iron stores and glucose intolerance at the third trimester in non-anaemic women. The role of iron excess in the pathogenesis of GDM needs to be examined.