Uterine Scar Niche

A uterine scar niche (caesarean scar defect) is a triangular or wedge-shaped indentation in the myometrium at the site of a previous caesarean scar, at least 2 mm deep.

• It is common after caesarean delivery and is symptomatic in a minority.
• Risk factors are labour before caesarean delivery, single-layer closure, retroflexed uterus and multiple caesarean sections.
• It causes postmenstrual spotting and can lead to caesarean scar pregnancy or scar rupture.

Brown bleeding or spotting for 2 or more days after menses, dysmenorrhoea, chronic pelvic pain, dyspareunia, infertility and, rarely, caesarean scar pregnancy.

• Examination is usually normal; tenderness over the scar is possible.
• Differential diagnosis: endometrial polyp, adenomyosis, endometritis, intrauterine device effect, cervical ectropion, endometriosis, caesarean scar pregnancy.
• Complications: chronic bleeding, infertility, caesarean scar pregnancy, placenta accreta, scar dehiscence or uterine rupture in later pregnancy.

Diagnosis is by transvaginal ultrasound or saline infusion sonography.

• Transvaginal ultrasound in the early follicular phase, or saline infusion sonography, measuring niche depth and residual myometrial thickness.
• Hysteroscopy showing a pouch with pooled blood.
• Pelvic MRI for complex defects.
• Pregnancy test; exclude infection and polyp.
• Document residual myometrial thickness (measure in millimetres) and the ratio to adjacent myometrium.

Reduce spotting with hormonal treatment, and repair or resect the niche when symptoms persist or fertility is affected.

• Supportive: reassurance; menstrual diary; analgesia; counselling on a future pregnancy.
• Pharmacological: combined oral contraceptive (ethinylestradiol 30 micrograms with levonorgestrel 150 micrograms) daily, taken continuously or cyclically, to reduce spotting; or levonorgestrel 52 mg intrauterine system. Tranexamic acid 1 g oral 8-hourly for up to 4 days (maximum 4 g in 24 hours) for heavy flow. Ibuprofen 400 mg oral 8-hourly with food (maximum 1.2 g in 24 hours) for pain. Doxycycline 100 mg oral 12-hourly for 7 days if endometritis is found.
• Procedures: hysteroscopic resection of the niche edge for women with residual myometrial thickness of 3 mm or more; laparoscopic or vaginal repair with excision and re-closure for thin niches (below 3 mm) or when fertility is wanted; surgery for caesarean scar pregnancy. Close the uterus in two layers at future caesarean delivery.
• Special groups: in pregnancy with a thin scar (below 2.5 mm) plan elective caesarean delivery at 36 to 37 weeks and scan for placenta accreta. Avoid oestrogen-containing pills in women with migraine with aura, smoking above age 35 or thromboembolism.
• Red flags: heavy bleeding, pain with positive pregnancy test, fever, signs of scar pregnancy.
• Follow-up: review at 3 months for bleeding; repeat ultrasound at 6 months after surgery; early ultrasound in any future pregnancy.