What is the deal with a pregnant lady going to kevarim? Is there any difference in regards to kivrei tzaddikim, such as Kever Rochel and the like?
There is no prohibition for a pregnant woman to visit kevarim. Some poskim debate the question of the wife of a kohen visiting kevarim during her pregnancy, but most authorities permit this. If she knows that she bears a boy, some prohibit visits to kevarim close to the end of term.
Sources: Even for a kohen’s wife, many maintain that it is permitted to visit kevarim for two reasons. 1) Safek-sefeika: The fetus might be a girl, and even if it a boy, it might be a nefel; 2) There is no prohibition of tumah for a fetus in its mother’s womb, because this is considered tumah belu’ah. In the light of the first rationale, some are stringent if an ultrasound has shown that the fetus is a boy. See Encyclopedia of Halachah and Medicine (Pregnancy) which cites many sources concerning this question.