Partial Placenta Previa

Partial placenta previa is a placenta that covers part of the internal cervical os, so that it covers the os only in part when the cervix is closed or dilated. It results from low implantation and, in a proportion, resolves as the lower segment grows. It matters because bleeding can be heavy and recurrent, the os may be uncovered or covered as dilatation changes, and vaginal birth is unsafe when any placenta covers the os.

• Risk factors: previous caesarean section, previous previa, multiple pregnancy, age above 35 years, smoking, assisted conception.
• Often found at the 20 week scan, with resolution in many before term.
• Caesarean birth is needed if any part of the os is covered at 36 weeks.

Women have painless bleeding in the second or third trimester, often small at first and recurrent, with a soft non tender uterus and malpresentation. Some have no symptoms.

• Bleeding after intercourse or exertion.
• Presenting part high.
• Differential diagnosis: placental abruption, marginal placenta, vasa previa, cervical polyp or ectropion, cervical cancer, show in labour.
• Complications: antepartum and postpartum haemorrhage, shock, anaemia, preterm birth, placenta accreta spectrum, hysterectomy, stillbirth, maternal death.

The approach is transvaginal ultrasound with repeat scans and no vaginal examination.

• Transvaginal ultrasound: placental overlap of the internal os of less than the full os, edge to os distance, bleeding or retroplacental clot; rescan at 32 and 36 weeks.
• Colour Doppler and MRI where available if previous caesarean section.
• Haemoglobin, group and cross-match (2 to 4 units), Kleihauer test in RhD negative women.
• Fetal growth and liquor at 28, 32 and 36 weeks.

The principle is surveillance, steroids if bleeding, and caesarean section at 37 to 38 weeks and 6 days, earlier for heavy bleeding.

• Supportive: avoid intercourse and strenuous work; two cannulae when admitted for bleeding; blood in the bank; left lateral rest; transfusion for haemoglobin below 7 g/dL or shock; teach to attend at once for any bleeding.
• Pharmacological: ferrous sulphate 200 mg oral 8-hourly for anaemia; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 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 for bleeding, repeated once after 30 minutes if needed; 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.
• Procedures: caesarean section at 37 to 38 weeks and 6 days when the os is still partly covered at the 36 week scan, and at once for heavy bleeding; balloon tamponade, compression sutures, uterine artery ligation or hysterectomy for uncontrolled bleeding; vaginal birth is attempted only if the repeat scan shows the placental edge 11 mm or more from the os.
• Special groups: RhD negative women give anti-D immunoglobulin 500 IU IM within 72 hours of each bleed; previous caesarean section with suspected placenta accreta spectrum needs tertiary care with blood and surgical teams.
• Red flags: bleeding soaking more than 2 pads in an hour, shock, contractions with bleeding, abnormal fetal heart rate.
• Follow-up: ultrasound at 32 and 36 weeks; haemoglobin every 4 weeks; antenatal review every 2 weeks; postnatal haemoglobin and iron for 3 months.