Your Period: When Is It OK to Skip and When Is It Not?

Skipping periods frequently comes up during discussions with my patients. It seems like most women who have regular periods are reluctant to skip them for a medical indication, usually having the perception that there will be a negative health consequence, while the ones who have never had regular periods perceive it as normal. The truth is that they're both wrong.

The best way to understand skipping periods is to understand a little about a normal menstrual cycle. Basically, in order to have a regular cycle, you have to ovulate. The first half of the cycle (starting with the onset of your period), your body goes through a complex sequence of hormonal signaling to promote the maturation of an egg. During that time, your ovaries produces a lot of estrogen, which stimulates the growth of the endometrium (the lining of the uterus). Midway through, you ovulate, and your ovaries then switch gears and start producing not only estrogen but also progesterone. I think of progesterone as the brakes--it tells the endometrium to stop growing and to mature for a possible pregnancy instead. If you do not conceive that cycle, after 14 days, the ovaries' hormone production system poops out, and your hormone levels drop abruptly. This triggers your period to start because hormones are no longer available to support the endometrium.

Whether or not it's OK to skip periods is really a matter of whether or not your endometrium is getting progesterone exposure. Before menopause, regardless of ovulation, most women's ovaries will continue to make some estrogen. If that continues over time without any progesterone (i.e., no braking signal), the lining can get overgrown, and eventually the over-stimulated endometrial cells can start showing changes that can lead to cancer. This is more problematic in overweight women because it turns out that fat cells also produce some estrogen (a weaker type than is made in the ovary).

What I usually tell my patients is that if we have a good reason for them not having periods, then it's OK, and all of those good reasons involve progesterone exposure. This includes having long-term progesterone therapy, such as with the Depo Provera shot, Implanon, or Mirena IUD. It is also true for patients who are on birth control pills, as these contain a type of progesterone as well, in combination with estrogen. In the case of the pill, most packs are designed to give patients a monthly period by providing either 4 or 7 days of a placebo (sugar pill), which mimics the end of an ovulatory cycle--triggering a period by abrupt withdrawal of hormones. By skipping those placebo pills, a woman can safely skip her period. This is how extended-cycle pills like Seasonique and Lybrel work (Seasonique gives you a period at the end of 3 months; Lybrel skips your period every month). With all of these medications, because of the continuous progesterone exposure, the endometrium becomes very thin--the brakes are always on--so there is no "build-up" of tissue as many patients fear. In the case of some, such as the Mirena, you might stop your period entirely simply because there is no significant amount endometrium to shed.

However, skipping periods naturally is not OK. It indicates some problem with a woman's hormonal signaling, which is causing her not to ovulate and, therefore, not to produce progesterone. While this is not unusual in the late 40's as women approach menopause, it is clearly abnormal before that time. As I explained earlier, most women continue to produce estrogen, and this can have disastrous consequences for the uterus. In addition to the worst-case scenario, cancer, long-term "unopposed estrogen exposure" (meaning all estrogen, no progesterone) can also cause women to have very heavy periods or even periods more than once a month. Aside from problems with the uterus, when we evaluate women for skipping their periods, we sometimes find other hormonal problems, such as thyroid disorders, which can have implications for a woman's general health. For all of those reasons, if you do not have regular periods, you should see a doctor to help you figure out why. This is particularly true if it has been going on for a long time; if you just skip one cycle and then go back to your usual thing the next month, don't sweat it.

In a nutshell, progesterone is good, and you can use it to your advantage if you want to skip periods. But if you're not using it and skipping periods anyway, that's not good; see your doctor.