Endometrial Stroma Location and Fibroids: What to Know

Understanding where the endometrial stroma sits inside the uterus—and how fibroids interact with it—can clarify why some people develop heavy periods, fertility challenges, or pelvic symptoms. This guide explains the anatomy in plain language, how fibroids affect the uterine lining, what symptoms to watch for, and the current, evidence-based options for diagnosis and treatment.

Quick anatomy: Where is the endometrial stroma?

The uterus has three main layers: the inner lining (endometrium), the muscular wall (myometrium), and the outer serosa. The endometrium itself has two parts: glands and stroma—a supportive, cell-rich connective tissue that nourishes the glands and responds to hormones. The stroma is arranged in two layers:

• Functional layer: Thickens under estrogen and progesterone each cycle and sheds during menstruation.
• Basal layer: Anchored near the myometrium; it regenerates the functional layer after each period.

During early pregnancy, the stromal cells undergo decidualization—a transformation that supports embryo implantation and early placental development. Healthy stromal function is therefore central to normal menstruation and fertility.

What are fibroids—and where do they grow?

Uterine fibroids (leiomyomas) are benign growths that arise from smooth muscle cells in the myometrium, not from the endometrium or its stroma. Their location determines how much they affect the endometrial lining:

• Submucosal fibroids: Grow just beneath the endometrium and can protrude into the uterine cavity, directly distorting or compressing the lining and its stroma.
• Intramural fibroids: Grow within the myometrial wall; larger ones can indirectly affect the cavity.
• Subserosal fibroids: Project outward from the uterus; these generally affect periods less and are more likely to cause bulk symptoms (pressure, pelvic discomfort) when large.

Fibroids are common, especially during the reproductive years. Many cause no symptoms, but some are associated with heavy menstrual bleeding, pelvic pressure, pain, and, in specific circumstances, fertility or pregnancy complications.

How fibroids can affect the endometrial stroma

Although fibroids originate in the myometrium, their proximity to the uterine cavity can influence the endometrium and its stroma in several ways:

• Distortion of the uterine cavity: Submucosal fibroids can stretch or ulcerate the endometrial surface, increasing the area that sheds and provoking heavy or prolonged periods.
• Altered blood flow: Fibroids can disrupt normal uterine vascular patterns, contributing to heavier bleeding.
• Changes in stromal function: Research suggests submucosal and large intramural fibroids may interfere with normal hormonal signaling, receptivity, and stromal decidualization, potentially affecting implantation in some patients.

Most fibroids do not cause infertility. However, submucosal fibroids and some sizeable intramural fibroids that deform the cavity are linked with subfertility and miscarriage risk; addressing them may improve outcomes for certain patients trying to conceive.

Important distinction: Fibroids are different from endometrial stromal tumors

Because the words sound similar, it’s worth emphasizing: fibroids are benign muscle tumors. Endometrial stromal sarcomas are rare cancers that arise from stromal tissue itself and behave very differently. Most people with heavy bleeding or pelvic pressure have benign fibroids, not stromal tumors. Suspicion for sarcoma is typically based on unusual imaging features, rapid growth in postmenopause, or other red flags and requires specialist evaluation.

Symptoms to watch for

• Heavy menstrual bleeding (soaking pads/tampons in under 2 hours, passing large clots, anemia symptoms like fatigue or shortness of breath)
• Prolonged periods or bleeding between periods
• Pelvic pressure, bloating, frequent urination, constipation, or lower back pain
• Pain with intercourse
• Difficulty conceiving or recurrent pregnancy loss (especially with cavity-distorting fibroids)

How clinicians evaluate the lining and fibroids

• Pelvic exam: May detect an enlarged or irregularly shaped uterus.
• Transvaginal ultrasound: First-line imaging to identify fibroids and assess size and location.
• Saline infusion sonohysterography (SIS): Injecting sterile saline during ultrasound outlines the uterine cavity, improving detection of submucosal fibroids and polyps.
• MRI: Helpful for complex cases, surgical planning, or when the number and location of fibroids need precise mapping.
• Hysteroscopy: A small camera is passed through the cervix to directly visualize the cavity; submucosal fibroids can often be treated during the same procedure.
• Endometrial sampling: May be done to evaluate abnormal bleeding and rule out other causes when indicated.

Treatment options: Tailored to symptoms, goals, and location

Not everyone with fibroids needs treatment. Management depends on symptoms, fibroid size and position, age, and pregnancy plans.

Conservative and medical options

• Watchful waiting: Reasonable for mild or no symptoms; periodic monitoring with exams and ultrasounds.
• NSAIDs: Can reduce menstrual cramps and modestly lower bleeding.
• Tranexamic acid: A non-hormonal option taken during menses to reduce heavy bleeding.
• Hormonal therapies: Combined hormonal contraception or progestin-only methods may lighten periods. A levonorgestrel-releasing intrauterine device (LNG-IUD) can substantially reduce bleeding for many, provided the cavity isn’t significantly distorted.
• GnRH agonists/antagonists: Temporarily reduce estrogen to shrink fibroids and decrease bleeding. FDA-approved oral combination therapies such as elagolix/estradiol/norethindrone (Oriahnn) and relugolix/estradiol/norethindrone (Myfembree) are indicated for heavy menstrual bleeding associated with fibroids. These are typically used for defined durations with monitoring due to potential hypoestrogenic side effects (e.g., hot flashes, bone density loss).

Procedural and surgical options

• Hysteroscopic myomectomy: Minimally invasive removal of submucosal fibroids through the cervix; often first-line for bleeding and fertility concerns tied to cavity-distorting fibroids.
• Myomectomy (laparoscopic, robotic, or open): Removes fibroids while preserving the uterus; appropriate for those aiming to maintain fertility. Recurrence can occur.
• Uterine artery embolization (UAE): Interventional radiology procedure that shrinks fibroids by cutting off their blood supply; helpful for bleeding and bulk symptoms. Not typically first choice when future pregnancy is a priority.
• MRI-guided focused ultrasound (MRgFUS): Noninvasive thermal ablation option for selected patients.
• Hysterectomy: Definitive treatment when childbearing is complete and other options are unsuitable or unsuccessful.

Your clinician will consider the fibroid’s location relative to the endometrial stroma and cavity when recommending therapy. For example, removing a submucosal fibroid that deforms the lining often yields the greatest improvement in heavy bleeding and may improve chances of conception in select patients.

When to seek care

• Periods that are consistently heavy, prolonged, or accompanied by anemia symptoms
• Bleeding between periods or after sex
• Pelvic pressure or pain that affects daily life
• Difficulty conceiving after 6–12 months of trying, or recurrent pregnancy loss
• Rapidly worsening symptoms, new postmenopausal bleeding, or concerns about a rapidly enlarging mass

Key takeaways

• The endometrial stroma is the supportive tissue within the uterine lining that is essential for menstruation and implantation.
• Fibroids arise from the uterine muscle, but submucosal and some intramural fibroids can disrupt the stroma and cavity, leading to heavy bleeding and, in some cases, fertility issues.
• Accurate mapping of fibroid location guides treatment—especially if fertility is a goal.
• Effective therapies range from medications to minimally invasive procedures and surgery; choices should be individualized.

References and trusted resources

• NICHD, NIH. Uterine Fibroids: Condition Information. https://www.nichd.nih.gov/health/topics/uterine/conditioninfo
• MedlinePlus, NIH. Uterine Fibroids. https://medlineplus.gov/uterinefibroids.html
• ACOG. Uterine Fibroids (Patient FAQ). https://www.acog.org/womens-health/faqs/uterine-fibroids
• NCBI Bookshelf (StatPearls). Histology, Endometrium. https://www.ncbi.nlm.nih.gov/books/NBK554450/
• NCBI Bookshelf (StatPearls). Uterine Leiomyoma. https://www.ncbi.nlm.nih.gov/books/NBK546680/
• FDA. Approval of Oriahnn for heavy menstrual bleeding due to fibroids. https://www.fda.gov/news-events/press-announcements/fda-approves-first-oral-drug-treatment-management-heavy-menstrual-bleeding-associated-uterine-fibroids
• FDA. Myfembree (relugolix/estradiol/norethindrone) information. https://www.fda.gov/drugs
• NCI. Uterine Sarcoma Treatment (PDQ) – Patient Version. https://www.cancer.gov/types/uterine/patient/uterine-sarcoma-treatment-pdq

This article is informational and not a substitute for personal medical advice. Discuss your symptoms and goals with a qualified clinician.