Is nuvaring effective the first month after an abortion?

I had an abortion 3 and 1/2 weeks ago and began nuvaring 4 days after my abortion. My boyfriend and I have been using condoms the last few days with the birth control though. I would like to know when Nuvaring becomes effective? Though we're using condoms, tonight one broke in the middle of intercourse so we opened and used a new one but we aren't sure when it broke and I'm aware pregnancy can be caused by pre-nut. Real, and credible advice please ! Thanks !!