Impact of Gestational Hypothyroidism on Exclusive Breastfeeding in the Early Postnatal Period

Background: Exclusive breastfeeding (EBF) provides health benefits, yet its continuation remains limited. Maternal endocrine disorders, including gestational hypothyroidism, may impair lactogenesis through hormonal dysregulation; however, evidence regarding the association between gestational hypothyroidism and breastfeeding outcomes remains limited. Objective: To investigate the association between maternal gestational hypothyroidism and breastfeeding outcomes in term infants, with a focus on EBF at the end of the first month and formula-free breast milk feeding at 6 months. Methods: This retrospective matched case–control study compared term infants of mothers with gestational hypothyroidism treated with levothyroxine ( n = 103) and matched controls ( n = 103). Feeding data were obtained from medical records and 6-month telephone follow-up, and factors associated with early formula supplementation were analyzed using multivariable logistic regression. Results: EBF rates were significantly lower in the case group at 1 month (58.3% versus 81.6%, p < 0.001). Formula supplementation within the first postnatal day was more frequent in the case group than in controls (46.6% versus 21.4%; χ 2 = 14.63, p < 0.001). At 6 months, formula feeding—either alone or combined with breastfeeding and/or complementary foods—was significantly more frequent in the case group (45.6% versus 25.2%, p = 0.003). Among infants who ever received formula ( n = 84), formula was initiated during the first postnatal month more frequently in the case group (82.7% versus 59.4%, p = 0.018), with earlier mean age at formula initiation (1.4 ± 0.97 versus 2.3 ± 1.51 months, p = 0.003). Multivariable logistic regression showed that higher maternal gravidity was independently associated with early formula supplementation (odds ratio = 3.16; 95% confidence interval: 1.09–9.10; p = 0.033). Conclusions: Gestational hypothyroidism was associated with lower EBF rates at 1 month and increased early formula supplementation. These findings underscore the need for targeted lactation support and careful postpartum follow-up in mothers with gestational hypothyroidism.