Pelvic tilting poses may be performed during all three trimesters of pregnancy. However back-lying pelvic tilts should be limited to the first trimester.
After the fourth or fifth month a pregnant woman lying on her back may become uncomfortable, dizzy, or even nauseous. This is due to the weight of the uterus pressing down on a vein called the vena cava. The vena cava brings blood back to the heart from the legs and pelvis. When it is compressed, blood volume to the heart decreases, blood pressure drops, and blood flow to the mother’s brain and the placenta is lessened. This causes temporary oxygen deprivation to mother and child. If this should happen, the mother would become light-headed. To stop the dizziness, she would need to roll onto her side and sit up.
The vena cava syndrome is most pronounced in the last trimester of pregnancy. Therefore, all back-lying poses are to be discontinued after the fifth month.
It is important to prevent straining the abdominal muscles during pregnancy. They are already being overstretched by the growing uterus. To avoid overworking these muscles when sitting up, roll onto one side, and use your hands to push yourself up to a sitting position.