Reproductive system · Pelvis · Female
Myometrium !
The myometrium is the thick muscle wall of the uterus; it contracts in labour to push the baby out and then clamps the vessels to stop bleeding.
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What it is
The thick smooth-muscle wall of the uterus.
What it does
Contracts in labour and clamps the vessels after birth to stop bleeding.
Key facts
- Where
- Thick smooth-muscle wall of the uterus (inner longitudinal, middle interlacing vascular, outer longitudinal layers)
- Blood supply
- Arcuate and radial branches of the uterine artery
- Nerve
- Uterovaginal plexus (from inferior hypogastric plexus): sympathetic T10–L1, parasympathetic S2–S4
- Function
- Contractions of labour (oxytocin); after birth the interlacing fibres clamp the vessels ('living ligatures')
Relations
- Superficial
- Perimetrium (serosa) over the body and fundus; at the sides the broad ligament, from which the uterine artery sends arcuate branches into the vascular middle layer
- Deep
- Endometrium, with no submucosa between them
Examination
- Bimanual examination: a fibroid uterus is enlarged, firm and irregular; a uterus with adenomyosis is evenly enlarged, softer and tender
- Fundal palpation after birth: a firm, contracted uterus at or below the umbilicus is normal; a soft, boggy, high uterus means atony
On imaging
Ultrasound shows fibroids as well-defined, usually hypoechoic masses that cast shadows. T2-weighted MRI maps their number and position before surgery (well-defined and dark) and shows adenomyosis as a thickened junctional zone (often quoted as over 12 mm).
Common problems
- Fibroids (leiomyomas) grow from it.
- Poor contraction after birth (uterine atony) is the main cause of heavy bleeding after delivery.
How it is diagnosed
Pelvic examination and ultrasound (often transvaginal); hysteroscopy or a sample of the lining (biopsy) when needed; MRI for some cases.
Treatment
- Medicines or a hormonal intrauterine device for heavy bleeding.
- Removal of fibroids (myomectomy) or blocking their blood supply (embolisation).
- Hysterectomy (removal of the uterus) when other treatments are not enough or for cancer.
- Caesarean section to deliver a baby through the abdomen.
Clinical notes
- Atony is managed in steps: fundal massage and bimanual compression with uterotonic drugs, then compression sutures, uterine or internal iliac artery ligation or embolisation, and hysterectomy as the last resort
- Myomectomy removes fibroids and keeps the uterus; a deep myometrial scar can rupture in a later labour
- Uterine artery embolisation shrinks symptomatic fibroids by cutting off their blood supply
- Red degeneration: a fibroid outgrows its blood supply in pregnancy, causing acute localised pain
Memory aid
Causes of postpartum haemorrhage, the 4 Ts: Tone (atony, the commonest), Trauma, Tissue (retained placenta) and Thrombin (clotting problems).
Related conditions
- Postpartum haemorrhage
- Placental abruption
- Uterine fibroids (leiomyomas)
- Endometrial cancer
- Adenomyosis
- Abnormal uterine bleeding
- Dysmenorrhoea
- Preterm labour and birth
- Puerperal infection (postpartum endometritis and maternal sepsis)
- Placenta accreta spectrum
- Uterine rupture
- Gestational trophoblastic neoplasia (choriocarcinoma)
Test yourself
Think of the answer, then tap the question to see it.
What is the commonest cause of postpartum haemorrhage, and how does the myometrium normally prevent it?
Uterine atony (Tone, first of the 4 Ts); normally the contracting myometrium clamps the vessels after birth.
Which factors increase the risk of myometrial atony after birth?
An overdistended uterus (twins, excess fluid, large baby), long or very fast labour, infection, fibroids and a retained placenta.
Which fibroids, by position, are most linked with heavy bleeding and infertility?
Submucous fibroids, which bulge into the uterine cavity.
How does a uterus with adenomyosis differ from a fibroid uterus on bimanual examination?
Adenomyosis: evenly enlarged, softer and tender (globular). Fibroids: enlarged, firm and irregular.
What is red degeneration of a fibroid?
In pregnancy a fibroid outgrows its blood supply, causing acute localised pain.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- myometrium TA2 3520
- Official Spanish (DeCS)
- Miometrio DeCS D009215
- English (TA2)
- Myometrium
- Also called
- muscular coat of uterus
Related
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Abdomen and Pelvis: Uterus.
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Representative model, for educational purposes only.
