There are chances of getting pregnant even even though you release seminal fluid outside vagina. When you get excited, some slimy lubricating fluid (prostatic fluid) flow in penile urethra that may contain some sperms which enter vaginal tract during intercourse before proper ejaculation happens. Also there maybe some sperms remained in penile urethra from previous Ejaculation. There are maximum chances of getting pregnant in the mid cycle days  of menstrual cycle. If your cycle is of 28 days (1st day to be counted on the day menstrual flow starts) the 14th day bears the maximum chances of getting pregnant. On the both sides of 14th day chances of conceiving gradually decreases with minimum chance (not zero ) near 1st and 28th day of cycle.