The stretch marks are caused by an abrupt expansion of the tissues. When the expansion is very gradual stretch marks are practically non existent.
An individual's elasticity varies.
Some patients develop stretch marks from growth spurts during puberty, muscle tissue gain from weight lifting and pregnancy. Some individuals never develop stretch marks and still others are very prone to them.
Mature stretch marks are very difficult to remove. You can tell a stretch mark is mature by the age of course and by the color - which is usually white. Deep fissures which are purple in color can scarcely be removed with treatments short of excision. This means that those microdermabrasion treatments that you have been getting are probably going to do nothing but empty your pocket book. The white marks CAN be darkened using a flesh-colored pigment implanted using micropigmentation.
There is still no successful treatment for the removal of stretch marks. Some swear by Shea nut butter, others, olive oil. Some swear by Retin A as a solution to the red lines that may develop in the early stages of stretch mark formation. Ask your surgeon before doing anything other than what he or she instructs. There is no guarantee that stretch marks will not develop but medical science has faith that a proven method of removal will be discovered, eventually.