Objective: To evaluate whether breastfeeding in women with type 1 diabetes mellitus is associated with a decreased insulin requirement.
Methods: In this prospective study conducted between September 2006 and August 2008, type 1 diabetic pregnant women were recruited before the third trimester of pregnancy. Eligible women had no evidence of diabetes-related complications and were treated with continuous subcutaneous insulin infusion pump therapy. During pregnancy and in the first 8 weeks of the postpartum period, participants performed daily fingerstick blood glucose monitoring with at least 12 measurements per day; insulin dosages were adjusted to maintain normoglycemia. Participant characteristics, diabetic parameters, and neonatal growth were compared between women who breastfed exclusively and women who did not breastfeed.
Results: Of 18 women, 12 breastfed and 6 did not. Compared with nonbreastfeeding mothers, breastfeeding mothers showed a decreased need for total daily basal insulin (0.21 +/- 0.05 units/kg per day vs 0.33 +/- 0.02 units/kg per day). The mean value of total daily basal insulin was significantly lower in the breastfeeding group than in the non-breastfeeding group. The mean number of hyperglycemic episodes in the first 2 weeks post partum and during the third to eighth weeks was not different between the groups. However, the mean number of hypoglycemic episodes in the first 2 weeks post partum in the breastfeeding group was significantly higher than in the nonbreastfeeding group (11.9 +/- 2.6 episodes vs 5.5 +/- 1.6 episodes, P<.001). No differences were observed between the groups in neonatal birth weight or infant weight after 8 weeks of age.
Conclusions: Decreased need in total daily basal insulin is caused by increased glucose use during lactation. We recommend that the starting total daily basal insulin dosage for type 1 diabetic women who breastfeed be calculated as 0.21 units times the weight in kg per day. This regimen results in normoglycemia and minimizes the risk of severe hypoglycemia associated with lactation.