it is not possible for you fall pregnant while having your period, this is because the endometrium in which the egg follicle lays, is shed. You can only fall pregnant when you ovulate and that is only possible for 24 hours. So if you were considering having unprotected sex although it is not advised the easiest way is to find out when in the month you ovulate and avoid having unprotected sex in this period of time.

Yes!! It is possible to get pregnant while you are on your period. This is taken from ivillage, and the same question was asked then answered by a certified nurse midwife--

"the simple answer to this is yes. If a woman has a short cycle -- typically 21 days from first day to first day -- then she is actually ovulating on day seven of her cycle (the seventh day from the first day of her period). Because some periods last that long, it is possible that a menses may be just ending when she is ovulating.

Also, some bleeding may not be necessarily a real period. Occasionally, ovulation can cause some spotting, which can be mistaken for a period. A woman may think she is safe just at the most unsafe time.

Bleeding may represent implantation of a fertilized ovum, too.

It is best to see a health care provider to get all of this straightened out. Dates, ovulation and pregnancy are best handled with you, your wife and your provider sitting together with a calendar between you. "