As long as there is enzyme and hydrogen peroxide present in the solution, the reaction continues and foam is produced. Once one of both compounds is depleted, the product formation stops. If you do not add dish soap to the reaction, you will see bubbles generated but no stable foam formation.
Probably Mary's doctor will not doctor a chronic villus sampling because of her first time pregnancy at the aged of 37 and her doctor ordered so many series of routine screening procedure. The doctor will not order a chronic villus sampling on Mary.
