Aims/hypothesis: Hypoglycaemia in association with breastfeeding is a feared condition in mothers with type 1 diabetes. Thus, routine carbohydrate intake at each breastfeed, particularly at night, is often recommended despite lack of evidence. We aimed to evaluate glucose levels during breastfeeding, focusing on whether night-time breastfeeding induced hypoglycaemia in mothers with type 1 diabetes.
Methods: Of 43 consecutive mothers with type 1 diabetes, 33 (77%) were included prospectively 1 month after a singleton delivery. Twenty-six mothers (mean [SD] age 30.7 [5.8] years, mean [SD] duration of diabetes 18.6 [10.3] years) were breastfeeding and seven mothers (mean [SD] age 31.7 [5.6] years, mean [SD] duration of diabetes 20.4 [6.2] years) were bottle-feeding their infants with formula. All were experienced in carbohydrate counting using individually tailored insulin therapy with insulin analogues (45% on insulin pump, 55% on multiple daily injections). Thirty-two women with type 1 diabetes, matched for age ±1 year and BMI ±1 kg/m2, who had not given birth or breastfed in the previous year, served as a control group. Blinded continuous glucose monitoring (CGM) for 6 days was applied at 1, 2 and 6 months postpartum in the breastfeeding mothers who recorded breastfeeds and carbohydrate intake at each CGM period. CGM was applied at 1 month postpartum in the formula-feeding mothers and once in the control women. The insulin dose was individually tailored after each CGM period.
Results: The percentage of night-time spent with CGM <4.0 mmol/l was low (4.6%, 3.1% and 2.7% at each CGM period in the breastfeeding mothers vs 1.6% in the control women, p = 0.77), and the breastfeeding mothers spent a greater proportion of the night-time in the target range of 4.0-10.0 mmol/l (p = 0.01). Symptomatic hypoglycaemia occurred two or three times per week at 1, 2 and 6 months postpartum in both breastfeeding mothers and the control women. Severe hypoglycaemia was reported by one mother (3%) during the 6 month postpartum period and by one control woman (3%) in the previous year (p = 0.74). In breastfeeding mothers at 1 month, the insulin dose was 18% (-67% to +48%) lower than before pregnancy (p = 0.04). In total, carbohydrate was not consumed in relation to 438 recorded night-time breastfeeds, and CGM <4.0 mmol/l within 3 h occurred after 20 (4.6%) of these breastfeeds.
Conclusions/interpretation: The percentage of night-time spent in hypoglycaemia was low in the breastfeeding mothers with type 1 diabetes and was similar in the control women. Breastfeeding at night-time rarely induced hypoglycaemia. The historical recommendation of routine carbohydrate intake at night-time breastfeeding may be obsolete in mothers with type 1 diabetes who have properly reduced insulin dose with sufficient carbohydrate intake.
Trial registration: ClinicalTrials.gov NCT02898428.
Keywords: Breastfeeding; Carbohydrate counting; Continuous glucose monitoring; Gestational weight gain retention; Hypoglycaemia; Insulin dose; Insulin pump therapy; Type 1 diabetes.