Recall that managers are tasked with ensuring the success of organized entities operating in a volatile and partly-unobservable economic environment. Deliberate influence over the success of such an organization requires access to information necessary to analyze causal relationships, sufficient integrity of their organizations sufficient to implement their resulting plans of action, and sufficient stability of conditions to ensure that the implementation is still relevant at the time of implementation.
Informing your manager that you are transsexual means that you are informing them of something of which they have little understanding (lack of information), which is in transition (lack of stability), and which is unfamiliar to the other members of their organization (threatening the organizational morale). In short, you are informing them of an additional risk without an associated reward. Therefore, you have reason to conceal that information until they have enough experience with you to trust the quality of your work (stability), the team is familiar with you (organizational morale), and you have earned sufficient respect and patience that you may impose upon the boss's time to inform him of the nature of transition (information).
Good luck.
- N