If the pregnancy was already mentioned as in your example "If a persona is pregnant, ...", you could say:
- irrespective of how many months.
- no matter how far along.
- no matter the trimester.
Since you're saying "irrespective of", using "trimester" as in the third option is probably the best. "trimester" is not in months or days, but because you're saying "the duration or stage doesn't matter", I think it conveys the same idea succinctly.