No. They start out life as basically unsexed females. When they choose a sex, the ones who become male become male (or some reasonable facsimile thereof).
Exactly how male is left unknown. They can get women pregnant but despite being male, no male children have ever been born, so they're presumably still XX genetically. What's between the legs is essentially unknown (a brief summary of the changes a girl who chose to be male went through left it mysteriously absent). It's just as possible that they don't have p0n0s at all. But the breasts do go away and there's usually a growth spurt, providing a more masculine build.