Mid-pregnancy, perinatal, and neonatal reproductive endocrinology: a prospective cohort study in twins and singleton control subjects

Children from a twin are not overexposed to sex steroids at the time of birth, despite higher concentrations in their mothers, and girls from opposite sex twins do not show androgenic influences from their male co-twin. The female co-twin may influence the hypothalamic-pituitary-testicular axis of her brother via central inhibition.