It is not only important to do exercise in your normal routine. If you get pregnant the need of exercise even increased. The reason is that your muscles would get strengthen and you will feel less stress out. Abdominal exercises during pregnancy are safe and can be done if you are not going through any of the complications. You can also consult your health care practitioner in order to get to know which exercises you can do. In the first trimester of the pregnancy, sit ups and crunches are quite safe to be performed.