Bleeding is without a doubt the single most obvious miscarriage symptom. Cramping and bleeding together certainly make a miscarriage very likely. However, just cramping in the abdominal area, without the presence of bleeding, usually does not signify a miscarriage. As the uterus adjusts to its new situation and the embryo is implanting and then growing, it is totally normal and expected for a pregnant woman in her first trimester to experience some degree of abdominal cramping. If you are experiencing light, menstrual like cramps, without any of the other symptoms that indicate a miscarriage (most notably bleeding!) the chances are that you have no reason to worry.
Something that may put your mind at ease is going to a prenatal appointment and hearing your baby's heartbeat, either through ultrasound or doppler. If you are worried about cramping, feel free to call your healthcare provider that is what they are there for! Later in pregnancy, cramping may in fact be something called round ligament pain, which is not unusual in pregnant women. Do watch out for rhythmic cramping which, as you may have guessed, may point to preterm labor. Preterm labor can, in fact, be halted in many cases with the use of medication. Therefore, from your second trimester or so, it is important to head in to the ER or the maternity ward if you are experiencing labor contractions, or think you may be having contractions.