Complete Placenta Previa

Complete placenta previa is a placenta that covers the whole of the internal cervical os. It results from low implantation, often over a uterine scar. It matters because it carries the highest risk of heavy antepartum bleeding, requires caesarean birth, and is often accompanied by placenta accreta spectrum when there is a previous caesarean section.

• Risk factors: previous caesarean section, previous previa, multiple pregnancy, age above 35 years, smoking, assisted conception, multiparity.
• First bleed commonly occurs at 28 to 34 weeks.
• Vaginal birth is not possible.

Women have painless fresh red bleeding, often recurrent and increasing, with a soft non tender uterus and malpresentation. Some have no bleeding until labour or term.

• Bleeding at rest or after intercourse.
• High free floating presenting part.
• Differential diagnosis: placental abruption, vasa previa, cervical lesion, show in labour, genital trauma, uterine rupture, low lying placenta.
• Complications: massive haemorrhage, shock, anaemia, preterm birth, placenta accreta spectrum, hysterectomy, DIC, postpartum haemorrhage, stillbirth, maternal death.

The approach is ultrasound confirmation of a placenta covering the os on transvaginal scan, with no vaginal examination.

• Transvaginal ultrasound: placenta covering the internal os with an overlap measured in millimetres; rescan at 32 and 36 weeks.
• Colour Doppler and MRI where available for accreta spectrum, especially with previous caesarean section.
• Haemoglobin, blood group and cross-match (4 units), coagulation screen if heavy bleeding, Kleihauer test in RhD negative women.
• Ultrasound for fetal growth and liquor at 28, 32 and 36 weeks.

The principle is admission at the first bleed or from 34 weeks, steroids, anaemia correction and planned caesarean section at 36 to 37 weeks and 6 days.

• Supportive: admit after a bleed until birth where distance or transport is a problem; two cannulae; blood in the bank; pelvic rest; left lateral rest; avoid vaginal examination; transfusion for haemoglobin below 7 g/dL or shock.
• Pharmacological: ferrous sulphate 200 mg oral 8-hourly; ferric carboxymaltose 15 mg/kg (maximum 1000 mg) IV once after 13 weeks if haemoglobin stays below 9 g/dL; betamethasone 12 mg IM twice, 24 hours apart, from 24 weeks to 34 weeks and 6 days when delivery within 7 days is likely; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; tranexamic acid 1 g IV over 10 minutes at bleeding or caesarean section, repeated once after 30 minutes if bleeding continues; cefazolin 2 g IV before incision; oxytocin 10 IU IM at birth then infusion of 20 IU in 1 litre sodium chloride 0.9 percent at 125 mL per hour for 4 hours; carboprost 250 micrograms IM every 15 minutes (maximum 8 doses) for atony, avoided in asthma; misoprostol 800 micrograms sublingual for atony.
• Procedures: elective caesarean section at 36 to 37 weeks and 6 days, at once for heavy bleeding; skin and uterine incision chosen by placental site; uterine balloon tamponade, compression sutures, uterine artery ligation or hysterectomy for uncontrolled bleeding; no digital examination under any circumstances.
• Special groups: RhD negative women give anti-D immunoglobulin 500 IU IM within 72 hours of each bleed; placenta accreta spectrum needs birth at 34 to 36 weeks in a tertiary unit with 4 to 6 units of blood; women who decline transfusion need iron optimised and cell salvage.
• Red flags: bleeding soaking more than 2 pads in an hour, systolic blood pressure below 90 mmHg, pulse above 110 per minute, contractions with bleeding, abnormal fetal heart rate.
• Follow-up: antenatal review every 2 weeks; haemoglobin every 4 weeks; ultrasound at 32 and 36 weeks; postnatal haemoglobin at 24 hours with ferrous sulphate 200 mg oral 8-hourly for 3 months.