Sex assignment at birth
Sex assignment at birth is neither biological nor psychological, but a peculiar Romish cultural custom attaching a supernatural significance to a "birth certificate" is used by city hall in the municipality or locality of one's birth.
Biologically, sex is determined at conception, not at birth, but liberal doctors and scientists with a Democratic Party political agenda are not willing to admit that life begins at conception.
Before conception, the father's gametocytes undergo meiosis, and divide into haploid spermatozoa, one of which fertilizes the mother's ovum. It is the spermatozoon's sex chromosome, either X or Y, that determines the sex of the zygote which then develops into the embryo by mitosis.