Pre-Cum

i was messing around with my boyfriend and as a tease he inserted the head of his penis in me for maybe 30 seconds before i got off. he had no condom on, we didn't have sex before that and he didn't ejaculate when i gave him a blowjob before (only pre-cum). he said there was no pre-cum when be put it in either but guys can't really control whether or not that happens, so therefore i figure he can't be sure. i'm not on birthcontrol (getting an iud soon) and was wondering if i should be okay? also wondering in general in what cases can you get pregnant from pre-cum?