In a situation in which a married woman is not considered
niddah, she is permitted to immerse in a mikveh without a bracha on any night she pleases. In your case, assuming that you are not in
niddah, that would be permissible. Many women have a custom of immersing at the ninth month of their pregnancy.
We cannot evaluate whether or not you are in
niddah from the bleeding episodes you describe without detailed information. If you have any question in this regard, please get back to us with details. We recommend consulting with a halachic authority whenever there is light bleeding to assist you in evaluating your halachic status.
Note that it is possible for a woman to become pregnant the first time she ovulates during or after breastfeeding – without having a menstrual period before conceiving. The fact that you are pregnant does not in itself mean that the light bleeding you experienced was a period.
