This trimester is called the fetal stage. The third trimester runs from week 29 to week 40. During this trimester, the baby's skeletons are fully formed, but still soft and fragile. Throughout the fetal phase, babies will gain about half a pound per week. By the end of the third trimester, the baby's organs are ready to function independently. Mothers, on the other hand, experience many changes. First, she will have shortness of breath, swollen extremities, the breast will begin to leak colostrum. Additionally, she will have problems sleeping. Additionally, she will experience contractions, which will often be false labor.