Helix Clinic blog

Many women who are worried about their f ertility will use an ovulation predictor kit to see if they are ovulating ok. A common query that we encounter is about how reliable the kits are. If the result appears postive, does that necessarily mean that ovulation has occurred?

The thing to remember is that ovulation kits predict impending ovulation by detecting the surge of a hormone called LH, or luteinizing hormone. LH is the catalyst that thrusts the egg out of the ovary during ovulation. When the basal body temperature rises as a result, ovulation has occurred because after ovulation, the leftover follicle (the corpus luteum) that encased the egg in the ovary starts producing progesterone, a heat-inducing hormone.

So, the progesterone causes the basal body temperature to rise, usually a day or two after ovulation, and there is usually a two or three day delay from the LH surge to the temperature rise. The LH surge happens first, then ovulation, and then the temperature rise.

This means that it is possible to have an LH surge and then still not ovulate.  If this happens, the ovulation predictor kit will register positive but the body temperature will not rise to a sustained higher level. This is why it is a good idea to track the temperature as well as use the ovulation predictor kit.

Tags: basal body temperature, fertility, infertility, ovulation