Prenatal hormones and sexual orientation Only 23% of childhood gender problems will result in transsexuality in adulthood. Drawing on some transsexualism cases, Garcia-Falgueras and Swaab state that "[f]rom these examples it appears that the direct action of testosterone on the developing brain in boys and the lack of such action on the developing brain in girls are crucial factors in the development of male and female gender identity and sexual orientation ... ." Countless studies have been run on peripheral levels of sex steroids in male and female homosexuals, a considerable number of which claimed to find "less 'male hormone' and/or more 'female hormone' in
Transgender hormone therapy (male-to-female) in girls. Conversely, high levels of progesterone, in conjunction with other hormones such as prolactin, are responsible for the lobuloalveolar maturation of the mammary glands during pregnancy. This allows for lactation and breastfeeding after childbirth. Although progesterone causes the breasts to change during pregnancy, the breasts undergo involution and revert to their pre-pregnancy composition and size after the cessation of breastfeeding. Every pregnancy, lobuloalveolar maturation occurs again anew. There are two types of progestogens: progesterone, which is the natural and bioidentical hormone in the body; and progestins, which are synthetic progestogens. There are dozens of clinically used progestins. Certain progestins,