Exercising while you're pregnant is great for you and your baby-to-be-but there are exceptions to every rule! After your first trimester, It's important to understand that the only thing that sits between your baby and external forces is a thin layer of tissue. For this reason, you need to avoid any contact sports that might cause someone (or something) to run into your abdomen. So basketball, rugby, and soccer are all out. Similarly, horseback riding and skiing are no-nos, as you don't want to risk a fall. Scuba diving is another definite no-no during pregnancy, as too much water pressure puts your baby at risk for decompression sickness. In addition, certain sports may be safe for women who are already experienced in them, but are definitely not OK to begin during pregnancy. These include mountain biking, roller blading, tennis, and fast running. Newbies to exercise should leave these potentially dangerous sports to the pregnant pros and engage in safer forms of exercise, like brisk walking or yoga. And remember, no matter what your routine, check with your doctor before exercising!