Reproductive · PANCE / PANRE

Placenta Previa

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Placenta covering or near the internal cervical os — painless bright red bleeding in second/third trimester.

Also known as: placenta previa, low-lying placenta, marginal previa, complete previa

Overview

Placenta implanted over (complete previa) or within 2 cm of (low-lying placenta) the internal cervical os in the late second or third trimester. The 2012 Society of Maternal-Fetal Medicine simplified terminology eliminated 'partial' and 'marginal' in favor of complete vs low-lying.

Epidemiology

Affects ~1 in 200 deliveries at term (many low-lying placentas identified earlier migrate as pregnancy progresses). Risk rises with cesarean delivery history.

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Question 1ReproductiveEasy
A 35-year-old female G3P2002 with a prior cesarean delivery presents at 36 weeks with a single episode of painless bright red vaginal bleeding that has since stopped. She is hemodynamically stable, and the fetal heart rate tracing is reassuring. Ultrasound shows a placenta completely covering the internal cervical os. Which of the following is the most appropriate management?
  • AExpectant management until 39 weeks
  • BVaginal delivery with continuous fetal monitoring
  • CPlanned cesarean delivery at 36-37 weeks
  • DImmediate cesarean delivery
Reveal answer & full explanation
Correct answer: C — Planned cesarean delivery at 36-37 weeks
  • AExpectant management until 39 weeks
  • BVaginal delivery with continuous fetal monitoring
  • CPlanned cesarean delivery at 36-37 weeks✓
  • DImmediate cesarean delivery

Why Planned cesarean delivery at 36-37 weeks is correct

  • Placenta previa is defined as the placenta covering the internal cervical os, and classically presents with painless bright red third-trimester bleeding
  • Risk factors include prior cesarean, prior uterine surgery, advanced maternal age, and multiple gestations
  • For a stable patient whose bleeding has resolved, ACOG recommends scheduled cesarean delivery at 36 0/7 to 37 6/7 weeks to balance prematurity risk against the risk of a future catastrophic bleed
  • Digital pelvic exam is contraindicated because it may provoke massive hemorrhage; betamethasone is given if preterm delivery before 37 weeks is anticipated

Why the others are wrong

  • Expectant management until 39 weeks — waiting to term is unsafe in previa because the longer the wait the higher the chance of a life-threatening hemorrhage; delivery is planned preterm at 36-37 weeks (anchoring on term delivery)
  • Vaginal delivery with continuous fetal monitoring — contraindicated, as cervical dilation over the placenta causes massive hemorrhage regardless of monitoring (right-concept-wrong-route)
  • Immediate cesarean delivery — reserved for uncontrolled hemorrhage, non-reassuring fetal status, or hemodynamic instability, none of which are present once bleeding has stopped and mother and fetus are stable (premature closure)

Additional high-yield points

  • Distinguish from placental abruption (painful bleeding) and vasa previa (fetal vessels over the os with risk of fetal exsanguination)
Question 2ReproductiveEasy
A 32-year-old female at 28 weeks gestation presents with painless vaginal bleeding. She has no contractions and the fetus is in cephalic presentation. Her prior cesarean delivery was 2 years ago. Ultrasound shows the placenta completely covers the internal cervical os. Which of the following is the most appropriate management?
  • AInitiation of intravenous tocolytics with bed rest and daily fetal nonstress testing
  • BImmediate emergency cesarean delivery with maternal transfusion and neonatal resuscitation
  • COutpatient expectant management with pelvic rest and strict bleeding precautions
  • DInpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring
Reveal answer & full explanation
Correct answer: D — Inpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring
  • AInitiation of intravenous tocolytics with bed rest and daily fetal nonstress testing
  • BImmediate emergency cesarean delivery with maternal transfusion and neonatal resuscitation
  • COutpatient expectant management with pelvic rest and strict bleeding precautions
  • DInpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring✓

Why Inpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring is correct

  • Complete placenta previa (placenta covers the internal cervical os) with active bleeding at 28 weeks warrants inpatient admission for close observation
  • The patient is currently stable (no ongoing hemorrhage, no non-reassuring fetal status), so expectant management—not immediate delivery—is appropriate to prolong gestation
  • Antenatal corticosteroids are given between 24 and 34 weeks to accelerate fetal lung maturity in anticipation of possible preterm delivery
  • Continuous maternal-fetal monitoring, type and screen, and IV access allow rapid escalation if bleeding recurs or becomes severe
  • Delivery is by planned cesarean (vaginal delivery is contraindicated with complete previa), typically at 36–37 weeks if the patient remains stable

Why the others are wrong

  • Initiation of intravenous tocolytics with bed rest and daily fetal nonstress testing — she has no contractions, so tocolysis is not indicated, and this plan omits the antenatal corticosteroids that are the priority at 28 weeks
  • Immediate emergency cesarean delivery with maternal transfusion and neonatal resuscitation — emergent delivery is reserved for uncontrolled hemorrhage or non-reassuring fetal status, and this patient is stable
  • Outpatient expectant management with pelvic rest and strict bleeding precautions — outpatient care is considered only after bleeding has stopped and the steroid course is complete; active bleeding from a complete previa at 28 weeks requires admission

Additional high-yield points

  • Presentation: painless vaginal bleeding in the second or third trimester (sentinel bleed); uterus non-tender and soft — contrasts with placental abruption (painful, tender, board-like uterus)
  • Placenta accreta spectrum: prior uterine scar plus previa creates high risk; evaluate with ultrasound and MRI; deliver at a center capable of managing massive hemorrhage; cesarean-hysterectomy may be needed
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Risk factors

  • Prior cesarean delivery (linear with number — 1% after one, ~3% after four)
  • Prior placenta previa
  • Advanced maternal age (>35)
  • Multiparity
  • Multifetal gestation
  • Smoking, cocaine use
  • IVF and assisted reproduction
  • Prior uterine surgery (myomectomy, D&C)

Pathophysiology

Implantation in the lower uterine segment, near or over the cervical os, makes the placenta vulnerable to disruption as the lower segment forms and the cervix effaces in late pregnancy. The thin lower segment cannot contract effectively to control bleeding from disrupted placental vessels.

Clinical presentation

Symptoms

  • Painless bright red vaginal bleeding in the second or third trimester (classic — sentinel bleed)
  • Often unprovoked; can follow intercourse
  • Bleeding may resolve spontaneously, recur, or be massive
  • Some are asymptomatic and detected on routine ultrasound

Signs / physical exam

  • Bleeding without abdominal pain or uterine tenderness
  • Soft, non-tender uterus
  • Fetal heart tones usually normal initially
  • Hemodynamic instability in massive bleeding

Classic findings

Third-trimester woman with painless bright red vaginal bleeding, soft non-tender uterus, and placenta over or near the cervical os on TVUS.

Differential diagnosis

  • Placental abruption — Painful bleeding, uterine tenderness, hypertonus; often dark blood; can be concealed; usually NOT preceded by sentinel painless bleed
  • Vasa previa — Fetal vessels traversing membranes over cervical os; rupture of membranes → fetal exsanguination; consider with velamentous cord insertion or accessory lobe
  • Cervical/vaginal lesion — Polyp, ectropion, cancer, lacerations; speculum exam (gentle, after previa excluded)
  • Labor (bloody show) — Small amount of blood-tinged mucus with cervical change
  • Uterine rupture — Severe pain, loss of fetal station, fetal distress; prior cesarean scar history

Diagnostic workup

Diagnostic criteria

AVOID digital cervical exam in any patient with third-trimester bleeding until placenta previa is excluded by ultrasound.

Labs

  • CBC, blood type and crossmatch, coagulation studies
  • Kleihauer-Betke if fetomaternal hemorrhage suspected and mother is Rh-negative

Imaging

  • Transabdominal ultrasound first, then transvaginal ultrasound — safe in placenta previa and more accurate; gold standard for diagnosis
  • Routine anatomy scan at 18-22 weeks identifies most cases; many low-lying placentas resolve by third trimester
  • Repeat ultrasound at 32 weeks for previa identified earlier
  • MRI if placenta accreta spectrum suspected (placenta previa + prior cesarean is high-risk)

Diagnostic algorithm

FeaturePlacenta PreviaPlacental Abruption
Bleeding characterPainless, bright redOften painful, dark
OnsetOften sentinel bleed, may resolveSudden, may be concealed
Uterine toneSoft, non-tenderFirm, tender, hypertonic
Fetal status (initially)Often reassuringOften nonreassuring (placental loss)
Diagnostic testTVUS (safe in previa)Clinical; CT/US may show retroplacental clot (low sensitivity)
CoagulopathyRare unless massive bleedCommon (especially concealed/severe)
Risk factorsPrior cesarean, prior previa, ART, smokingHypertension, trauma, cocaine, PROM, smoking
DeliveryCesareanVaginal or cesarean based on stability
Distinguishing placenta previa from placental abruption.

Treatment

First-line

  • Avoid digital cervical exam, intercourse, vaginal tampons
  • Activity restriction (modified — strict bedrest no longer recommended)
  • Hemodynamic stabilization with IV access, type and screen, transfusion as needed
  • Inpatient management for active bleeding; outpatient with strict precautions and proximity to hospital for asymptomatic patients
  • Antenatal corticosteroids (betamethasone) for fetal lung maturity if 23-34 weeks with bleeding
  • Anti-D immunoglobulin for Rh-negative women with any bleeding

Delivery planning

  • Cesarean delivery is required for placenta previa (complete or with edge <1-2 cm from os in late pregnancy)
  • Scheduled cesarean at 36 0/7 - 37 6/7 weeks for uncomplicated previa
  • Earlier delivery for recurrent bleeding, signs of preterm labor, or placenta accreta spectrum
  • Tertiary center delivery with blood products, anesthesia, and surgical backup

Placenta accreta spectrum (PAS) — when previa + prior cesarean

  • Multidisciplinary planning: gyn-onc, MFM, anesthesia, urology, interventional radiology
  • Scheduled cesarean hysterectomy at 34 0/7 - 35 6/7 weeks
  • Preoperative cell saver, balloon occlusion catheters in select centers
  • Massive transfusion protocol availability

Acute hemorrhage

  • ABCs, large-bore IV access, type and crossmatch 4+ units
  • Continuous fetal monitoring
  • If fetus <34 weeks: stabilize, give corticosteroids, expectant management if bleeding stops
  • If fetus ≥34 weeks or bleeding uncontrollable: emergent cesarean delivery
  • Massive transfusion as needed

Complications

  • Antepartum hemorrhage requiring transfusion
  • Preterm birth (often iatrogenic for hemorrhage control)
  • Placenta accreta spectrum (accreta, increta, percreta) — especially with prior cesarean — peripartum hysterectomy may be required
  • Postpartum hemorrhage from poorly contractile lower segment
  • Maternal mortality from hemorrhage
  • Vasa previa coexistence (rare)
  • Cord prolapse

PANCE pearls

  • NEVER perform a digital cervical exam in third-trimester bleeding until placenta previa is excluded by ultrasound.
  • Transvaginal ultrasound is safe in placenta previa and more accurate than transabdominal scanning.
  • Most low-lying placentas identified before 24 weeks 'migrate' as the uterus grows — repeat ultrasound at 32 weeks before final classification.
  • Placenta previa + prior cesarean delivery significantly raises placenta accreta spectrum risk (~25-67% with multiple cesareans + previa) — plan for cesarean hysterectomy.
  • Cesarean delivery is mandatory for complete placenta previa or low-lying placenta with placental edge within 1-2 cm of the os in late pregnancy.
  • Painless bright red bleeding is classic for previa; painful dark bleeding with uterine tenderness suggests abruption.

References

  • ACOG CO 764 — ACOG Committee Opinion 764: Medically Indicated Late-Preterm and Early-Term Deliveries
  • SMFM 2018 — SMFM Consult Series: Diagnosis and Management of Placenta Accreta Spectrum (Am J Obstet Gynecol 2018)
  • ACOG PB 234 — ACOG Practice Bulletin No. 234: Prediction and Prevention of Spontaneous Preterm Birth (relevant for management)

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Commonly confused with

vs Placental Abruption

Related Reproductive diagnoses

Polycystic Ovary Syndrome (PCOS)EndometriosisUterine Fibroids (Leiomyoma)Abnormal Uterine BleedingPrimary AmenorrheaSecondary AmenorrheaMenopausePelvic Inflammatory Disease (PID)Bacterial VaginosisCandidal VulvovaginitisTrichomoniasisCervical Cancer and HPVEndometrial CancerOvarian Cancer

Differentials & related conditions

Placental Abruption

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