Possibilities.?

My ex boyfriend and I had sex the very last day of my period last month. That morning I started my nuvaring ( I used it the month before also) I had it out for the week time it said to have it out. Anyways, my ex and I did not use protection but before he even came close to cumming he pulled out. What are the possibilities of becoming pregnant from pre cum?

We broke up about a week after this happen.