The effects of hypothyroidism on the fetal and neonatal IGF system have been well documented in thyroidectomized fetal sheep (Camm et al. 2021; Forhead et al. 1998; Forhead et al. 2002) and antithyroid drug‐treated rodents (Näntö‐Salonen et al. 1991; Elder et al. 2000; Näntö‐Salonen and Rosenfeld 1992). Here, IGF1 is linked to hypothyroidism.