If a woman or a man is compelled to expose their private parts to a female or male physician, this does not invalidate the fast. In the presence of a necessity (ḍarūra), it is permissible for a physician—whether male or female—to look at the private parts of a man or a woman.
However, in such circumstances, if a woman has access to a female physician, it is not permissible for her to consult a male physician; likewise, if a man has access to a male physician, it is not permissible for him to consult a female physician.
Nonetheless, even if this occurs, it does not fall under the acts that invalidate the fast.