What Meg said!
Some women who have never been overweight have tummy tucks done after they are done childbearing because of the muscle seperationg and skin laxity that
can come with pregnancy. Then there are some women (myself included) who have never been pregnant but have had skin laxity caused by massive weight loss.
But, not
all women who have been pregnant need tummy tucks, nor do
all people who have lost loads of weight need it.
Even with the two factors put together, not everyone will
need surgery, and even those who migh objectively need it choose not to get it done. It is a personal choice.
But, like Meg said, don't get concerned about such things that are far down the road! Focus on your health and continued weight loss (assuming that you are aiming for that) and when you reach your goal you can assess your body and determine what is right for you.