A fibroid diagnosis usually happens in one of two ways: you go to your GP because of symptoms, or fibroids are found incidentally during an unrelated scan. Either way, understanding what the tests actually show — and what their limitations are — helps you have a more informed conversation about what happens next.
Pelvic Ultrasound: The First-Line Test
Ultrasound is the standard initial diagnostic tool for fibroids. It is safe, quick, widely available, and provides a good picture of fibroid size, number, and location. There are two types:
Transabdominal ultrasound uses a probe moved over the lower abdomen with gel. It provides an overview of the uterus and surrounding structures. It is adequate for detecting larger fibroids but misses smaller ones, particularly submucosal fibroids inside the cavity.
Transvaginal ultrasound (TVUS) uses a small probe inserted into the vagina, positioned much closer to the uterus. It provides significantly better resolution — detecting smaller fibroids, mapping their location more precisely, and giving a clearer picture of whether any are distorting the uterine cavity. For women with fibroid symptoms, a transvaginal ultrasound is the more informative test. It is not uncomfortable for most women, though it can cause brief pressure.
If your GP has only performed a transabdominal scan, it is reasonable to ask whether a transvaginal scan would give a more complete picture — particularly if you are concerned about fertility or suspect submucosal involvement.
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Sonohysterography (Saline Infusion Sonography)
Also called SIS or saline sonogram. Sterile saline solution is injected into the uterine cavity through a thin catheter while a transvaginal ultrasound is performed simultaneously. The fluid creates contrast inside the cavity, making submucosal fibroids and uterine polyps much more visible than on a standard ultrasound.
This test is particularly useful when submucosal involvement is suspected, when fertility is being investigated, or when the standard ultrasound shows something ambiguous near the cavity. It is a short outpatient procedure — typically 10–15 minutes — with mild cramping that resolves quickly. Not all GP practices refer for this; it is more commonly available through gynaecology departments or fertility clinics.
MRI: The Most Detailed Picture
MRI is not the first-line test for fibroids — it is more expensive, less accessible, and not necessary in most straightforward cases. But it provides by far the most detailed information when the situation is complex.
MRI is typically used when: surgical planning is underway and the precise location of every fibroid matters; a fibroid is very large and the relationship to surrounding structures needs mapping; there is uncertainty about whether a mass is a fibroid or something else; or uterine fibroid embolisation (UFE) is being considered (MRI guides the procedure).
If you are being prepared for surgery or a major intervention, MRI is a reasonable thing to request — or to ask why it has not been recommended.
Hysteroscopy
A hysteroscope is a thin camera inserted through the cervix into the uterine cavity under direct vision. It allows a gynaecologist to see submucosal fibroids, polyps, and other intrauterine abnormalities directly — and often to treat them in the same procedure (hysteroscopic myomectomy removes submucosal fibroids directly through the hysteroscope).
Diagnostic hysteroscopy is usually performed when abnormal uterine bleeding has not been adequately explained by ultrasound, when polyps and fibroids need to be distinguished, or when fertility investigation requires direct visualisation of the cavity. It can be done under local anaesthetic in an outpatient setting or under general anaesthetic depending on complexity.
Blood Tests
Blood tests do not diagnose fibroids — but they are an essential part of the overall assessment:
- Full blood count (FBC): Checks haemoglobin and haematocrit — measures whether heavy bleeding has caused anaemia. Also checks platelet count which is relevant if surgery is being considered.
- Ferritin: Iron storage marker. Can be depleted before haemoglobin falls to clinically anaemic levels. Women with heavy periods often have normal haemoglobin but very low ferritin — explaining fatigue that does not show up on a basic blood test.
- Thyroid function: Thyroid disorders can cause heavy periods independently of fibroids — worth ruling out, particularly if periods changed around the same time as other thyroid symptoms.
- Hormone panel: Not always ordered but useful if the hormonal picture is unclear — FSH, LH, estradiol, and progesterone can inform the broader hormonal context.
Putting It Together
A complete diagnostic picture for fibroids typically involves at minimum: a transvaginal ultrasound confirming size, type, and location of all fibroids; a full blood count and ferritin to assess the impact of blood loss; and a clear conversation about what the findings mean for your specific situation.
If you have had only an abdominal ultrasound and a brief appointment, you may not yet have the complete picture. It is entirely appropriate to ask for a transvaginal scan, to request your ferritin be checked alongside haemoglobin, and to ask specifically about fibroid type and whether any are submucosal. For more on what to watch for and when to seek assessment, see our complete fibroid symptoms checklist.
