If you’ve ever had clots in your menstrual blood, you know you can’t really miss ‘em — they’re blobby, thick, chunky… and they may make you wonder what’s going on. After all, it’s not supposed to look like that, right?

Well, it depends.

What you’re seeing is just uterine lining, explains Dr. Sherry A. Ross, MD, a women’s health expert and author of She-ology: The Definitive Guide to Women’s Intimate Health. Period. “The actual blood you see on your pad or tampon is made from the lining of the uterus, also known as the endometrial glands,” explain Dr. Sherry. “The shedding of the endometrium contains fibrous tissue that can look like small pieces of liver or blood clots.”

How much blood there is and what it looks like varies from woman to woman and cycle to cycle. “The normal amount of blood loss is 4-12 teaspoons each cycle. This is also equal to an average of 35ml but can range from 10 to 80ml,” Dr. Sherry explains. Pretty big range — and that goes for consistency, too. “The consistency of the blood can be watery and stringy or fibrous. If this consistency is thicker, blood clots can develop.”

How much blood there is and what it looks like varies from woman to woman and cycle to cycle.

If you have a heavy flow, you may be very familiar with clots. “If your blood flow is heavy and leaves the uterus quickly blood clots are not usually created. If you have a heavy flow and blood leaves the uterus slowly, blood clots develop,” explains Dr. Sherry. As for the clots themselves, those range in size and shape a lot — and not all of them are cause for concern. “Small clots the size of raisins are usually nothing to worry about and can happen during a heavy blood flow,” she says. “Larger and thicker blood clots, greater than the size of a quarter, are reasons to be concerned.”

You’ll also want to keep an eye on your overall flow — if those clots accompany periods that are coming more frequently than every 21 days or lasting longer than 7 days for more than 3 months, that’s a sign that something may be wrong, says Dr. Sherry. Same goes for brown spotting that last longer than two or three months. And if clots are a new occurrence for you, that may be an indicator that something is not quite right too, says women’s health and functional nutrition coach Nicole Jardim.

If any of that sounds familiar, make an appointment with your doctor. Abnormal clots can signal fibroids, adenomyosis (a condition in which endometrial tissue grows into the uterine wall and can affect the ability of the uterine muscles to contract), or endometriosis, says Jardim. “These conditions are usually a sign that your body is in a state of estrogen dominance – which is really just another way of saying that your body is progesterone deficient.”

You’ll want a doc’s help figuring out what’s causing that estrogen dominance — extreme weight gain, hormonal imbalances, and stress are some of the possible culprits. And if you’ve been pregnant, you may be noticing more clots than usual, which isn’t necessarily indicative of a problem. “Your uterus may remain larger than it was previously, which can cause blood pooling and result in clots,” explains Jardim. And if there are polyps (common during pregnancy) blocking the regular flow of blood, there is an increased chance for clots as well, she says.

The best way to keep an eye on things? Use a period tracker, both Jardim and Dr. Sherry recommend. “You should be checking out your period to make sure it is coming on time and to see what the blood looks like,” says Jardim. You should also keep tabs on how you feel physically and emotionally during the week before and the week of your period.” Your body talks to you, so listen — and don’t hesitate to get your doctor’s opinion if you’re concerned.

Diana Vilibert is a freelance writer and copywriter living in Brooklyn, NY. She loves flea markets, martinis, to-do lists, traveling, and wearing leggings as pants. You can see more of her writing at www.dianavilibert.com and follow her on Twitter at @dianavilibert.