I agree with Tarobinc. Menstrual type cramps can be a sign of early labor. Talk to your ob; better to be safe than sorry.
Best bet is to run it by your OB as soon as you can.
It might be early labor. I have read where premature labor can feel like menstrual cramps. It could also be Braxton hicks but Im not sure.
If you have more than 4 cramps an hour, you should call your OB ASAP. That is what the OB nurse told me on Friday when I was having contractions showing on the monitor, although I didn't feel them.