Testosterone is the primary sex hormone in males. Its production starts when the male foetus is only two months old; at this stage the concentration is just as high as is normally found in men, right up until just before the birth. During this time testosterone stimulates the development of the male genitals. Testosterone levels drop just before birth and are just a little higher than girls have. The levels rise later on, and are just below the normal male level for three months, until it once again falls to a low level at the age of one. This increase in testosterone may be important for the normal development of the genitals during puberty. The level of testosterone stays the same from one until puberty.
Testosterone is also normally produced in a woman’s ovaries, but the level in the woman’s blood is only about five to ten per cent of that found in men.