Can You Get Pregnant During Your Period? Understanding Fertility & Cycle Timing

Question
I was wondering if it is possible for a woman to get pregnant while she is on her period? Lets say her period lasts four days.  At what point during those four days is she vulnerable to getting pregnant?.. and if she is not vulnerable during those four days at what point after does that chance kick in?  Thanks.

Answer
It depends on how long the whole cycle is.  Generally, from day 6 until day 18 the potential increases from just a little to very likely and then it stops being at all likely until your period starts.  So day 4 is probably not likely a day to get pregnant but day 8 or 10 would be more likely.