Conceiving/period question

봄하루 • Human wreckage

In the given scenario, let's pretend Sally gets her period very regularly. Let's say Sally has sex frequently before her period which is about in a week; Can she conceive before her period starts? How soon before? Does she miss her period or does it still pass til next month?

Sally isn't my hidden persona, i just had to figure out how to phrase the question without anyone taking it to heart 😅