Am I obligated to break my fast in Ramadan due to flank pain resulting from dehydration during my eighth month of pregnancy, given that there is no harm to the fetus, or should I intend to fast relying on God's help?

If the pain does not make fasting difficult, then breaking the fast is not permissible. But if fasting becomes difficult due to it, then breaking the fast is permissible, and making up the days (qada') becomes obligatory when able. The general rule is that fasting is obligatory for a pregnant woman. If she fears harm to herself or her fetus, then it is permissible for her to break the fast, and she must make up the days. If her fear is only for the fetus, then she must make up the days and feed one poor person for each day. If it is highly probable that she will be harmed by fasting, then breaking the fast is permissible; otherwise, it is not. There is no obedience to a creature in disobeying the Creator; therefore, there is no obedience to a husband or mother in breaking a fast that is obligatory to observe.