Roughly one in five women feel pain when they ovulate, although most don't recognize the cause. Mittelschmerz, German for middle pain, is ovulatory pain felt mid-cycle on one side of the lower abdomen.

The pain may switch from side to side, or stay on one side for several consecutive cycles, depending on which ovary is releasing an egg. The pain may be sharp, aching or cramping, is usually mild, and lasts from a few minutes to a few hours. Rarely, the pain is severe and continues for one or two days.

Mittelschmerz is generally understood to be caused by peritoneal irritation due to the ruptured follicular cyst. In other words, when the egg bursts out of the ovary, the bloody fluid leaking from the wound irritates the lining of the abdomen.

So now you know. If you own ovaries, the next time you feel a brief, vague pain on one side of your abdomen, consider where you are in your cycle. And then, if it be the case, update your Facebook status to "Mittelschmerzing."

I wish I didn't feel compelled to say this, but I do: relying on mittelschmerz as an indicator of ovulation, and avoiding sex for the following few days as a method of contraception, is not a good idea. Trust me, it's been tried.