A very good start toward minimising stretch marks is to get a good Vitamin E cream and add 10% by volume of an extract combination of the herbs Comfrey, Hypericum, Maritime Pine, Equisetum, Slippery Elm and Wheat Grass to it.
This cream can then be massaged daily into your tummy, perineum and upper thighs, or anywhere else you want your skin to be in top shape. It will support the elasticity of the skin during the stretching and allow it to spring back more effectively.
Massaging firmly and regularly is also part of the process and you should develop a program of doing this twice daily and keep it going as a routine.
Maybe enlist the aid of a lover or carer for this. You should also consider practicing perineal massage for the last three months also to get this area in shape and to minimize the need for cutting or the risk of tearing during the delivery. Get advice from your midwife or other professional, as to the best way to do this.