Often when we think of exercise during pregnancy, we think of cardio or maybe a low impact perinatal fitness class. Cardio during pregnancy can be healthy when approved by your OB or midwife; however, cardio is not the only exercise regimen that provides health and wellness. During the very first few days of pregnancy a hormone called relaxin is released. This hormone helps hip joints to have more flexibility and to help the pelvis expand and grow during pregnancy. Relaxin can cause hip joints to be sore sometimes.