The invention provides a method of making an optical fiber preform using a modified chemical vapor deposition process by flowing glass precursor gases through a preform tube for depositing glass material therein, and simultaneously flowing heavy water vapors through the preform tube for incorporating deuteroxyl groups into the glass material. Then, the preform tube is controllably heated so as to effect a collapse of the preform tube into a rod. Advantageously, optical fibers drawn from such preforms have an increased resistance to hydrogen and will not require passivation.