Well-controlled hypothyroidism does not affect the macronutrient composition of colostrum

Introduction Maternal hypothyroidism is a common endocrine disorder occurring during pregnancy and has been associated with adverse maternal and neonatal outcomes. When untreated or poorly controlled, hypothyroidism may influence lactation and milk composition, although the effects of well-controlled hypothyroidism on human milk remain insufficiently characterised. Methods This prospective cohort study included 120 postpartum women: 45 with well-controlled hypothyroidism treated with levothyroxine during pregnancy and 75 healthy controls. We collected colostrum samples within the first 5 days postpartum and analysed them using mid-infrared spectroscopy (MIRIS ® ) to determine macronutrient composition, including lipids, protein, carbohydrates, total solids, and energy content. We used the Mann–Whitney test for statistical analysis, with effect size assessed by Cliff’s delta. No a priori power analysis was conducted; therefore, interpret the results in light of the sample size and observed effect sizes. Results No significant differences were observed between the hypothyroid and control groups in any measured component of milk composition, including lipids, crude and true protein, carbohydrates, total solids, or energy content (for all components, the p value > 0.05). Effect sizes were negligible across all variables. Additionally, there was no significant difference in neonatal outcomes and maternal characteristics between groups, indicating appropriate clinical management of hypothyroidism during pregnancy. Discussion Well-controlled maternal hypothyroidism treated during pregnancy does not affect the macronutrient composition or energy content of colostrum in early lactation. The results indicate that adequate treatment of hypothyroidism does not affect the macronutrient composition or energy content of early colostrum. However, additional research to assess the composition of mature milk, the bio-active components and long term lactational outcomes must be done before wider implications for breastfeeding and human milk donation can be made.