Small chance of getting pregnant 1 week before your period, or is that chance no longer there?

Is there anyone who might know this? I was wondering if it still makes sense to have sex 1 week before your period to get pregnant, or are you no longer fertile by then? For example, 21 days after your period. Now I know that it probably doesn't make much sense, as I think in the week before, but I was wondering if there isn't a small chance. Greetings, Madelene