Placenta Praevia

Placenta praevia describes a placenta implanted wholly or partly in the lower uterine segment, classified on ultrasound by the relationship of the placental edge to the internal cervical os: placenta praevia (previously "major," covering the os), and low-lying placenta (placental edge within 20 mm of the internal os but not covering it, previously "minor").

Risk factors include previous cesarean section (risk rises with each prior section, and combined with an anterior low-lying placenta raises specific concern for placenta accreta spectrum), previous placenta praevia, multiparity, multiple pregnancy, and assisted conception.

Most cases are identified incidentally on the routine 18 to 20 week anomaly scan; a placenta appearing low at this stage is rescanned at around 32 weeks (placental migration with uterine growth resolves the majority)
Digital vaginal examination is contraindicated until placenta praevia has been excluded, given the risk of provoking catastrophic hemorrhage
Transvaginal ultrasound (safe and more accurate than transabdominal) confirms placental position and the precise relationship to the os
MRI is used in selected cases where placenta accreta spectrum is suspected (particularly with an anterior low placenta over a previous cesarean scar)

Asymptomatic placenta praevia confirmed after 32 weeks: plan cesarean delivery, typically around 36 to 37 weeks for placenta praevia covering the os, with timing individualized for a low-lying placenta not covering the os (vaginal delivery may be attempted if the edge is more than 20 mm from the os)
Acute bleeding: manage as major obstetric hemorrhage (see Postpartum Haemorrhage entry for the resuscitation principles, applied equally here): call for senior help, ABC assessment, two large-bore IV access, crossmatch, and admission for observation even if bleeding settles, given the high recurrence risk
Anti-D prophylaxis for any Rh negative woman with bleeding
Corticosteroids (betamethasone 12 mg IM x2, 24 hours apart) if preterm delivery is anticipated
Avoid intercourse and vigorous activity once diagnosed
Placenta accreta spectrum (abnormally invasive placenta, suspected on imaging with a history of previous cesarean and anterior low placenta) requires delivery planning at a specialist center with interventional radiology, blood bank, and surgical expertise available, given the very high hemorrhage risk; cesarean hysterectomy is often required

Referral: obstetric-led care for all confirmed cases; specialist placenta accreta spectrum service where suspected.

Clinical toolsCalculators

BMI GCS EDD Parkland Formula

Corrected Sodium Corrected Calcium Anion Gap Creatinine Clearance Insulin Calculations qSOFA Wells PE Wells DVT CHA₂DS₂-VASc HAS-BLED CURB-65 Centor/McIsaac

Placental Abruption

Premature separation of a normally sited placenta from the uterine wall before delivery, causing bleeding into the decidua basalis.

Risk factors include hypertension and pre-eclampsia (the strongest association), previous abruption, trauma, smoking and cocaine use, multiple pregnancy, polyhydramnios with rapid decompression (as with membrane rupture), and preterm premature rupture of membranes.

Classically painful vaginal bleeding with a tense, tender, "woody hard" uterus, in contrast to the painless bleeding of placenta praevia.

Bleeding may be revealed (visible vaginally) or concealed (retroperitoneal, behind the placenta, with disproportionately severe systemic signs relative to visible blood loss).

Fetal distress or fetal death may be the presenting feature in severe abruption.

Uterine contractions are frequently present, and preterm labor commonly follows.

Primarily clinical, based on the pain, tenderness, and bleeding pattern; ultrasound is poor at reliably detecting abruption (retroplacental clot is visualized in only a minority of cases) but is used to assess fetal wellbeing and exclude placenta praevia as an alternative cause of bleeding.

Cardiotocography assesses fetal status.

Coagulation profile is essential, given the risk of DIC, particularly with concealed abruption or fetal death, from release of thromboplastin into the maternal circulation.

FBC, group and crossmatch, Kleihauer test (quantifies fetomaternal hemorrhage, guiding anti-D dosing).

Managed as an obstetric emergency: senior obstetric and anesthetic involvement, ABC assessment, two large-bore IV access, aggressive fluid resuscitation, and crossmatched blood
Fetal status dictates urgency: a non-reassuring or absent fetal heart rate with maternal instability warrants immediate delivery, generally by emergency cesarean unless vaginal delivery is imminent
With a live fetus and reassuring CTG, continuous fetal monitoring and expedited delivery (mode depending on gestation, severity, and cervical status)
Intrauterine fetal death with abruption: vaginal delivery is generally preferred once the mother is stabilized, given the coagulopathy risk with cesarean in this setting, unless maternal condition mandates otherwise
Correct coagulopathy aggressively with fresh frozen plasma, cryoprecipitate, and platelets as guided by coagulation results and ongoing bleeding (see Postpartum Haemorrhage entry for detailed transfusion principles)
Anti-D prophylaxis for Rh negative women, dose guided by Kleihauer result where significant fetomaternal hemorrhage is suspected
Corticosteroids for fetal lung maturation if preterm and delivery is not immediately mandated

Referral: obstetric emergency requiring immediate senior obstetric, anesthetic, and neonatal involvement.

Placenta Praevia

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management