We considered various factors, including weight, smoking, alcohol, treatment with levothyroxine sodium, self-reported hypothyroidism or myxoedema, thyroid peroxidase antibody positivity, treatment with insulin product, self-reported systemic lupus erythematosis or SLE, age at menarche, and age-started oral contraceptive pill, as potential confounders of female infertility. Here, INS is linked to hypothyroidism.