Why Does BBT Spike and Ovulation Not Coincide?

Why does my ovulation kit say I am ovulating, but my basal body temperature doesn't have a rise at the same time?


Toni Weschler, MS

Toni Weschler is the author of the popular book Taking Charge of Your Fertility. By offering a simple and effective means of identifying... Read more

What you are experiencing is completely normal and to be expected. The ovulation kits predict impending ovulation by detecting the surge of a hormone called, LH, or luteinizing hormone. This hormone is the very catalyst that thrusts the egg out of the ovary during ovulation. The temperature shift indicates that ovulation has already occurred. Once you ovulate, the leftover follicle (the corpus luteum) that encased the egg in the ovary starts producing progesterone, a heat-inducing hormone. It is the progesterone that causes a thermal shift, or temperature rise in your body, usually a day or two after you ovulate. So in essence, you would expect to see about a two or three day delay from the LH surge to your thermal shift. The order is: LH, ovulation, then thermal shift. But keep in mind that it is possible to have an LH surge, but not actually ovulate. If this happens, you temperature will not rise in the form of a thermal shift.

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