There are many differences between being fat and pregnant; for one, a fat woman will always have her menstrual periods. You may be fat and pregnant at the same time, and that is why you will find it hard to know if a fat woman is pregnant. Anyhow, there are distinguishing signs of pregnancy, which will make the whole difference between pregnancy and fatness. First of all, a pregnant woman will not have her menstrual period. This has been the landmark sign of being pregnant, although you will not know with 100% certainty that you are pregnant if you do not have your periods. Some women will have some bleeding which they will take for periods when they are pregnant although this is not regular period bleeding. If you are healthy and in the right weight, you will know with certainty that you are pregnant when you miss your periods. Also, it has to be accompanied by symptoms such as general body tiredness, tender breasts and morning sickness. All of these can be explained in one word: human chronionic gonadotrophin hormone. This is the hormone that supports pregnancy, and its imbalance with the hormones in your body is what will cause you to have problems with morning sickness.