Endometriosis vs IBS: How to Tell Them Apart, and Why Many Women Have Both

Two common conditions that overlap

IBS affects about 12 percent of people in the United States, and women are up to twice as likely as men to develop it (NIDDK). Endometriosis affects roughly 10 percent of women and girls of reproductive age worldwide, about 190 million people (WHO). Both peak in the same decades of life and both produce bowel symptoms, so the two will often meet in the same woman by chance alone. The evidence says they meet more often than chance. In a UK primary care study of 5,540 women with endometriosis and four matched controls each, the odds of an IBS diagnosis were 3.5 times higher in the women with endometriosis, and the odds of receiving a new IBS diagnosis after endometriosis had already been confirmed were still 2.5 times higher (Seaman 2008).

From the IBS side: in a specialist IBS clinic in New Zealand, 36 percent of 160 women who met the Rome III criteria for IBS had endometriosis as well (Moore 2017). A referral clinic sees more complex cases than average, so this is not the rate for all women with IBS, but it shows how often the two sit together.

What IBS is: the Rome IV criteria

IBS is a diagnosis made from symptoms, using the Rome IV criteria published in 2016 (Mearin and colleagues). The criteria require recurrent abdominal pain on average at least one day per week over the past three months, associated with two or more of the following: the pain is related to having a bowel movement; it comes with a change in how often you go; or it comes with a change in the form of the stool. Symptoms must have started at least six months earlier. IBS is subtyped by the dominant stool pattern: constipation, diarrhea, mixed or unclassified. There is no visible damage to the bowel on colonoscopy or imaging.

Notice what the criteria do not mention: the menstrual cycle, pain with sex, or fertility. A woman can meet every Rome IV criterion and also have endometriosis, because the criteria describe a symptom pattern, not a cause.

Clues that point toward endometriosis

The NICE guideline NG73 lists the symptoms that should make a clinician suspect endometriosis: chronic pelvic pain; period pain that affects daily activities; deep pain during or after sex; period-related or cyclical bowel symptoms, especially painful bowel movements; period-related or cyclical urinary symptoms; and infertility together with any of these. Each one is a clue that a bowel complaint is not IBS alone.

• A cyclical pattern. Bowel symptoms that are clearly worse in the days before and during your period. In the New Zealand IBS clinic, bowel symptoms worsened by menstruation were significantly more common in the women who also had endometriosis (p = 0.0004) (Moore 2017).
• Deep pain with sex (dyspareunia). This was strongly associated of endometriosis among the IBS patients in the same study (p < 0.0001). Deep pain with sex is not a feature of IBS itself.
• Pain with bowel movements during periods (dyschezia), sometimes described as a stabbing pain in the rectum. A long-standing symptom of rectovaginal and bowel endometriosis.
• Painful periods severe enough to miss school, work or plans, from the teens onward.
• Difficulty conceiving. Endometriosis is found in a large share of women evaluated for infertility; IBS is not known to affect fertility.
• A family history. Having a first-degree relative with endometriosis raises your own risk (Zondervan 2020), and family history was significantly more common in the IBS patients who turned out to have endometriosis (p = 0.0003) (Moore 2017).
• Pain referred to the back, hip or down the leg, and urinary symptoms around your period.

Why the confusion happens

Bowel endometriosis sits on the outside of the bowel wall and rarely reaches the inner lining, so colonoscopy is usually normal. A normal colonoscopy plus cramping, bloating and altered bowel habit meets the definition of IBS. Unless someone asks how the symptoms relate to your cycle, the pattern goes unrecorded and the IBS label sticks. Both conditions also share visceral hypersensitivity, a nervous system that amplifies signals from the gut and pelvis, so treating one can leave the other unaddressed.

For a detailed guide to how endometriosis affects the bowel itself, see endometriosis bowel symptoms.

The workup for IBS

Rome IV describes IBS as a positive diagnosis made from the symptom pattern, with a limited set of tests to exclude other causes rather than an exhaustive search (Mearin 2016). Typical steps are a careful history, an abdominal examination, blood tests for anemia, inflammation and celiac disease, and stool tests to look for inflammatory bowel disease. Colonoscopy is reserved for alarm features such as bleeding, weight loss, anemia or onset after middle age. Treatment includes dietary change such as a low FODMAP diet, fiber or laxatives, antispasmodics, and medications that act on the gut-brain connection.

The workup for endometriosis

The ESHRE 2022 guideline recommends that endometriosis be suspected from the history and examination and that imaging, usually transvaginal ultrasound by an operator trained in endometriosis and sometimes MRI, be used to look for endometriomas and deep nodules, including on the bowel. Laparoscopy is no longer required to make the diagnosis, but it confirms the disease and treats it in the same operation. NICE NG73 adds that a normal examination, ultrasound or MRI does not rule endometriosis out, because superficial lesions are invisible on imaging. If you have an IBS diagnosis and any of the clues above, ask for this evaluation, ideally from a gynecologist who sees endometriosis regularly.

When both conditions are present, both need treating. In the New Zealand study, a four-week low FODMAP diet improved bowel symptoms by more than half in 72 percent of women with endometriosis and IBS, compared with 49 percent of those with IBS alone (Moore 2017), so gut-directed treatment may still help even when endometriosis is the underlying driver. Hormonal treatment or excision of bowel lesions addresses the endometriosis itself.

How tracking against your cycle helps the conversation

One of the most useful things you can bring you can bring to either a gastroenterologist or a gynecologist is a record that shows when your bowel symptoms happen relative to your period. Note each day: cycle day, bloating, cramping, stool pattern, pain with bowel movements, pelvic pain and any pain with sex, for at least two cycles. If the bad days cluster around menstruation, say so plainly; it reframes the question from "which IBS subtype" to "is this endometriosis". The PelviQuest app keeps period symptoms separate from daily symptoms so patterns around menstruation stand out; it is a screening and tracking aid, not a diagnosis.