No matter how big or small a sex difference, there is almost always significant overlap across distributions of men and women. In fact, estradiol, the predominant form of estrogen, is critical to sexual function for people who were assigned male at birth. Trans Survey from the National Center for Transgender Equality, only 15 percent of respondents identified as heterosexual.
Last year, ten physicians acquired this qualification and there is now growing interest from physicians and patients. The definition of sex was: "Sex refers to the biological and physiological characteristics that define men and women". PLoS One.