well if I remember rightly waaaaaaaaay back in catholic school " sex ed " they did say something about pre cum having a few swimmer in there so this is NOT and very good proventive, so we should all be good little girl and NOT have sex until we are married ( one girl in yr 11 was UTD and 2 or 3 by the end of yr 12 so didnt listen too well ) So I guess anything can happen I have heard of women getting pregnant on there last day of AF but not really of before your AF so I would be inclined to say you are NOT UTD sorry....

My sister is TTC ATM and has a few test with Very faint 2nd lines and she isnt UTD if I didnt know about her then I too would say a 2nd line is a line but now I know that sometimes its just a vap line or something....

Best of luck