There are many changes that occur in the body with pregnancy and large weight shifts. As the abdomen expands, the two stomach muscles that normally hold everything in flat can stretch and separate. After weight loss or delivery, the muscles do not always return to their original positions, and can leave residual looseness. Despite intensive exercise, muscles that are separated may never completely flatten the stomach. Similarly, as the abdomen expands, the skin stretches. If this occurs rapidly, the skin can tear and create stretch marks. After weight loss or delivery, the excess skin cannot shrink due to a loss of elasticity, and the skin in the lower stomach often drops and sags.
The third component is fat, and there are two types; superficial fat is the substance you can feel when you pinch the skin. Deep fat can accumulate underneath the muscle when you are overweight. If your only problem is superficial fat, and the skin and muscles have good tone, liposuction is all that is required. If it is a deep fat problem, diet is a must. If you have loose skin or muscle, an abdominoplasty, or tummy tuck is often the best option.