Halacha relies on one of three physical signs to determine when a woman becomes a niddah during labor:

1. At any point during or even before labor, uterine bleeding will make her niddah.

2. She becomes niddah at the point at which the contractions are so strong that she can no longer stand.

3. She becomes niddah at a certain degree of dilation, which is considered petichat hamakor (opening of the uterus). There is a range of opinions as to what degree of dilation establishes niddah status. The opinion of our site's rabbinic supervisor, Rav Yehuda Henkin is that full dilation establishes niddah status and there is no requirement to measure dilation.

Since an epidural can be given quite early in the process of labor, and you have no sensation of contractions getting stronger, you would rely on parameters one and three. At the point of full dilation, when you are ready to push, you are definitely a niddah. If you bleed at any time before that, you will be considered a niddah at that point. Again, this is Rav Henkin's postition. Note that other opinions exist in this matter, and you might want to consult with your rabbi about them.

We wish you an easy birth and Besha'ah Tovah!