This may be a tricky question, as you don't have to have surgery to
render a sex change. Use of hormones will also drastically alter
biological sex organs, and often surgery is not needed. In some
cases, surgery makes the change more permanent.
In modern times, several disorders related to gender have been
identified, each having a course of treatment that would fall under
the category of a sex change: Klinefelter's syndrom (extra X
chromosome), Turner's syndrome (missing X chromosome), Speck syndrome
(extra Y chromosome), hermaphrodotism (dual sex organs), and gender
dysphoria (feeling of being in the wrong body). All are treated with
hormones, and in the case of the latter two, surgery.
Babies that are born with sexually indeterminate organs are often
subjected to surgery at birth to render them as one or the other sex.
It is estimated that about 12,000 operations of this type take place
per year, and Congress recently had hearings in which persons who had
been subjected to this type of surgery voiced their opinion that the
doctors should have been required to wait until the age of consent to
conduct this surgery. Evidently this type of surgery has been
conducted for years prior to the adult voluntary sex change surgery,
but I don't know the year that began.
Sin,
Kathryn Aegis