Caesarean Scar Pregnancy

Caesarean scar pregnancy is implantation of the gestational sac in the myometrium at the site of a previous lower segment caesarean scar. It affects about 1 in 2000 pregnancies and is rising with caesarean rates. It can progress to uterine rupture, placenta accreta spectrum and major haemorrhage.

• Risk factors: one or more previous caesarean sections, scar niche.
• Usually diagnosed at 5 to 10 weeks.
• Early diagnosis allows conservative treatment.

Women may have painless vaginal bleeding or mild lower abdominal pain at 5 to 10 weeks after a caesarean delivery, or have no symptoms at all.

• Bleeding that worsens after instrumentation.
• Previous caesarean section is the key history.
• Differential diagnosis: inevitable miscarriage, cervical ectopic pregnancy, incomplete miscarriage, gestational trophoblastic disease, low implanted intrauterine pregnancy.
• Complications: uterine rupture, massive haemorrhage, hysterectomy, placenta accreta spectrum, death.

The approach is transvaginal ultrasound.

• Ultrasound: empty uterine cavity and cervical canal, gestational sac in the anterior lower uterine segment at the scar, thin or absent myometrium between sac and bladder (below 5 mm), prominent Doppler flow around the sac.
• Magnetic resonance imaging where available.
• hCG, haemoglobin, cross-match 4 units, blood group and Rhesus status.
• Avoid blind curettage.

The principle is to end the pregnancy early using treatment that controls bleeding and spares the uterus.

• Supportive: admission; two large-bore cannulae; blood available; counsel on risks of continuing the pregnancy.
• Pharmacological: methotrexate 50 mg/m2 IM single dose, or 1 mg/kg IM days 1, 3, 5 and 7 with folinic acid 0.1 mg/kg IM days 2, 4, 6 and 8; local injection of methotrexate 25 mg into the sac under ultrasound; hCG weekly to negative; tranexamic acid 1 g IV over 10 minutes for bleeding.
• Procedures: hysteroscopic or laparoscopic excision with repair of the scar; suction evacuation under ultrasound guidance with Foley balloon ready; uterine artery embolisation for heavy bleeding; hysterectomy if rupture or uncontrolled bleeding.
• Special groups: Rhesus negative women give anti-D immunoglobulin 250 IU IM within 72 hours; if the woman chooses to continue the pregnancy, planned caesarean hysterectomy at 34 to 36 weeks is usually needed.
• Red flags: heavy bleeding, pain, shoulder tip pain, collapse.
• Follow-up: hCG weekly until negative; ultrasound at 2 weeks and 6 weeks; early scan in future pregnancies; counsel on recurrence risk of about 5 percent.