Irregular menstrual cycles—defined as having cycles that are shorter than 21 days, longer than 35 days, or vary between extremes—are very common. Most women will have times when their periods get a little wacky due to illness, travel, or stress.
"Having the occasional irregular cycle is nothing to be concerned about," says Dr. Corrine Kolka Welt, MD, a reproductive endocrinologist at Massachusetts General Hospital and an assistant professor at Harvard Medical School. Still, according to a study led by Dr. Karen Barnard, MD, MPH, an associate professor of clinical internal medicine at the University of South Carolina School of Medicine, about 17 percent of women report experiencing consistently irregular cycles, which may have an effect on fertility or indicate a health concern.
"I've been having irregular cycles since college," said Ann Chavie of Chicago, Illinois, "I used to get my period every couple of weeks! Now, after being on the pill and then stopping to try to have a baby, I have really long cycles."
"My cycles are all over the place," said Ella Longoria [not her real name] of Denver, Colorado. She thought it was her demanding and erratic schedule as a resident physician that was making her cycles irregular. "But now that I'm an attending physician and I work regular hours, my cycles have not settled down," she said.
According to Dr. Welt, there are three very common reasons why a woman might be having irregular cycles:
- Being too thin or exercising too much
- Polycystic ovary syndrome (PCOS), which indicates disruption in the hormonal balance and is characterized by excessive hair growth, acne, and irregular cycles
- Early menopause
Other culprits behind irregular cycles can include thyroid problems or high levels of the hormone prolactin (which is normally present at high levels only when a woman is breastfeeding).