Create an optimal environment for fertilization Prefert ® is a lubricant for couples who want to have children, it is used during sexual intercourse during ovulation. During this time, the properties of the cervix and cervical mucus change. This is basic at the time of ovulation. The Prefert ® Vaginal Gel has the same pH value (7.0 to 7.4) as the cervical mucus during the fertile period.