Placenta Previa
Painless, bright red vaginal bleeding in the second half of pregnancy – treat as placenta previa until excluded by ultrasound. Never do a digital vaginal exam first.
Painless vaginal bleeding
Bright red blood
Soft, non-tender uterus
Exclude previa before vaginal exam
Definition & Pathophysiology
Placenta previa occurs when the placenta implants in the lower uterine segment and overlies or is close to the internal cervical os. It is a major cause of antepartum haemorrhage in the second half of pregnancy.
- Bleeding arises when the lower uterine segment thins and the cervix dilates:
- Marginal placental vessels are torn.
- Bleeding is maternal in origin.
- Bleeding episodes may be:
- Recurrent but self-limiting early on.
- Massive and life-threatening if labour starts or the placenta is disturbed.
Placenta over / near os
Bleeding from lower segment stretching
Risk Factors
- Advanced maternal age.
- Multiparity.
- Previous caesarean section or uterine surgery (scarring).
- Prior miscarriages or induced abortions.
- Smoking.
- Multiple pregnancy.
- History of placenta previa in a previous pregnancy.
Previous C-section
Multiparous
Smoker
Clinical Features
- Bleeding:
- Classic: painless, bright red vaginal bleeding in 2nd or 3rd trimester.
- May be recurrent, often spontaneous, unrelated to contractions.
- Pain / uterus:
- Uterus usually soft and non-tender.
- Contractions may be absent or mild; some uterine irritability in a minority.
- Maternal status:
- Degree of shock usually correlates with visible blood loss.
- Foetus:
- Foetal heart usually present in early bleeds, but may show distress with heavy or ongoing bleeding.
- Malpresentation (e.g. transverse / breech) is more common.
Key rule: Any painless second- or third-trimester bleed must be
treated as placenta previa until excluded by ultrasound.
Diagnostic Testing
- Ultrasound:
- Gold standard for diagnosis and localisation of the placenta.
- Transabdominal scan for initial assessment.
- Transvaginal ultrasound is more accurate to define relationship to the internal os and is safe in experienced hands.
- Ensure bladder appropriately filled/emptied as per local protocol to avoid overcalling previa.
- Laboratory:
- FBC, group & crossmatch, coagulation screen.
- Baseline Hb and platelets.
Ultrasound before vaginal exam
Transvaginal scan gives best localisation
Vaginal Examination – Critical Safety Point
Never perform a digital vaginal examination in a patient with antepartum bleeding until placenta
previa is excluded by ultrasound. Probing the cervix can tear the placenta and cause catastrophic
haemorrhage.
- Speculum examination may be considered in a monitored setting if:
- Previa has been excluded, or
- Bleeding source is uncertain and obstetric team is present.
ED Management & Initial Stabilisation
Priorities in ED: resuscitate the mother, assess foetal status, avoid provoking further bleeding,
and involve obstetrics early.
- Maternal stabilisation:
- Two large-bore IV lines.
- Resuscitate with crystalloids; prepare blood products if bleeding is significant.
- Monitor BP, HR, RR, SpO₂, urine output.
- Send bloods: FBC, group & crossmatch, coagulation screen.
- Foetal assessment:
- Foetal heart with Doppler or CTG (if viable and available).
- Rh status:
- Rh-negative patients require anti-D immunoglobulin as per local protocol.
- Obstetric involvement:
- Immediate obstetric consultation for any late-pregnancy bleeding.
- Arrange ultrasound to confirm placental location.
Stability & Disposition
Mild bleeding, both stable
- Bleeding has stopped or minimal; vitals stable; reassuring foetal status.
- Confirm placenta location by ultrasound.
- Admit to obstetric unit for observation and further planning.
- Pelvic rest: no vaginal exams, intercourse, or strenuous activity.
Ongoing bleeding / concern
- Ongoing or recurrent bleeding; maternal vitals stable or slightly abnormal; foetus viable.
- Resuscitate, crossmatch, continuous foetal monitoring.
- Obstetrics to decide:
- Expectant management vs early delivery depending on GA and severity.
Severe bleeding / instability
- Heavy bleeding, maternal shock, or foetal distress/demise.
- Full resuscitation with fluids and blood products.
- Urgent obstetric decision for expedited delivery – usually emergency caesarean section if foetus viable.
- Prepare for high-care/ICU post-delivery if significant haemorrhage or coagulopathy.
- Definitive management: timing and mode of delivery (often planned caesarean for major placenta previa) are decided by obstetrics based on gestation, bleeding pattern, and foetal status.
Ongoing & Definitive Management
- For confirmed placenta previa:
- Expectant management with hospitalisation if recurrent bleeding and foetus preterm but stable.
- Planned caesarean section at appropriate gestation for major previa (placenta covering or very close to os).
- Vaginal delivery may be considered only in:
- Minor/low-lying placenta that has migrated away from the os by term, and
- No significant bleeding or other contraindications.
Management requires close coordination between obstetrics, anaesthesia, neonatology, and sometimes ICU, as placenta previa can be associated with heavy haemorrhage and complex operative delivery.
Resuscitate mother → then refine plan
Ultrasound before vaginal exam
Call obstetrics early for all antepartum bleeds