[RPG] What are the rules for determining pregnancy

I think handling it like they do in James Bond movies is the best thing. The romance leads to the beginning of the event and then fade to black...

I would definitely follow up within the story. Obviously, these two characters now have strong feelings for each other. They will now have emotional entanglements and all that. Jealousy, protective instincts, fear for the other character's safety, etc. There were two characters in one of my campaigns that were intimate (offscreen) and they roleplayed these issues as you might expect.

Player's Handbook II (3.5) / Divine Conversion / p193

This is a sidebar at the bottom of the referenced page, which is part of a section on rules for retraining. If you don't have the book, here is the direct quote:

DIVINE CONVERSION

As noted in the Player’s Handbook, a cleric who grossly violates the code of conduct imposed by his deity loses all spells and class features and cannot attain any more levels as a cleric of that deity. All these penalties remain in effect until he atones. But what if he doesn’t want to atone? What if a cleric of Hextor finds new meaning and purpose in serving Heironeous after a dramatic conversion experience? Such a character need not become a multiclass ex-cleric of Hextor/cleric of Heironeous. Instead, Heironeous can simply reinstate the character’s cleric powers once he has proven his loyalty, talent, and ability.

A cleric who changes his patron deity must complete a quest to prove his devotion to his new patron. The nature of the quest depends on the deity, and it always clearly reflects the deity’s alignment as well as his or her goals and beliefs. To start the process, the cleric must voluntarily accept a geas/quest spell cast by a higher-level cleric of his new deity. During the quest, the cleric has no access to spells or cleric class features—except his weapon and armor proficiencies, which he does not forfeit.

Upon completing the quest, the cleric receives the benefit of an atonement spell from a cleric of the new deity. The character then becomes a cleric of the new deity and is inducted into the clergy during an appropriate ceremony of the DM’s choosing. After selecting two of the new deity’s domains in lieu of his old ones, the character has all the powers and abilities of his previous cleric level, plus the granted powers of his new domains.

This method is the only one by which a cleric can change his deity. The retraining rules can’t be used to accomplish this task—it is simply too substantial a change in the character’s identity (not to mention his source of power) to chalk up to a bit of practice in his off hours.

This answer essentially reflects the ruling already found in the Forgotten Realms Campaign Setting, but it may be useful to know it's also located in a setting-independent rulebook, just in case there are any sticklers out there.