Precum- Okay or nah?

So I've been hooking up with this guy who doesn't exactly enjoy condoms so he's been doing the "pull-out" method. That's been fine, but what I'm worried about is the precum that he has when he enters me. Is this enough to get me pregnant? We definitely don't want to get pregnant, and I know we aren't being the safest about it, but I just wanted to know how effective precum can be. Thanks!