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 simplified terminology of the 2012 NICHD-led Fetal Imaging Workshop (co-sponsored by SMFM, ACOG, and AIUM, among others) 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?
ACesarean delivery after lung maturity testing
BVaginal delivery with continuous fetal monitoring
CImmediate cesarean delivery
DExpectant management until 39 weeks
EPlanned cesarean delivery at 36-37 weeks
Reveal answer & full explanation
Correct answer: E — Planned cesarean delivery at 36-37 weeks
ACesarean delivery after lung maturity testing
BVaginal delivery with continuous fetal monitoring
CImmediate cesarean delivery
DExpectant management until 39 weeks
EPlanned cesarean delivery at 36-37 weeks✓
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)
Cesarean delivery after lung maturity testing — amniocentesis to document lung maturity was once used to time late-preterm delivery, but ACOG advises against using fetal lung maturity testing to guide a medically indicated delivery: previa warrants delivery at 36-37 weeks regardless of the result, and testing only adds delay (superseded practice)
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
CInpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring
DOutpatient expectant management with pelvic rest and strict bleeding precautions
EAntenatal corticosteroids with scheduled cesarean delivery 48 hours after the final dose
Reveal answer & full explanation
Correct answer: C — 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
CInpatient admission with antenatal corticosteroids and continuous maternal-fetal monitoring✓
DOutpatient expectant management with pelvic rest and strict bleeding precautions
EAntenatal corticosteroids with scheduled cesarean delivery 48 hours after the final dose
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
Antenatal corticosteroids with scheduled cesarean delivery 48 hours after the final dose — tempting because steroids are given in anticipation of preterm delivery and some obstetric conditions are delivered once the course is complete, but this patient is stable, so the goal is to prolong gestation; delivering at 28 weeks adds the morbidity of prematurity, and planned cesarean is typically deferred to 36-37 weeks if she remains stable.
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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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
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
Feature
Placenta Previa
Placental Abruption
Bleeding character
Painless, bright red
Often painful, dark
Onset
Often sentinel bleed, may resolve
Sudden, may be concealed
Uterine tone
Soft, non-tender
Firm, tender, hypertonic
Fetal status (initially)
Often reassuring
Often nonreassuring (placental loss)
Diagnostic test
TVUS (safe in previa)
Clinical; CT/US may show retroplacental clot (low sensitivity)
Coagulopathy
Rare unless massive bleed
Common (especially concealed/severe)
Risk factors
Prior cesarean, prior previa, ART, smoking
Hypertension, trauma, cocaine, PROM, smoking
Delivery
Cesarean
Vaginal 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 when the placenta covers the internal os; with a low-lying placenta (edge within 2 cm of the os) a trial of labor may be offered, especially when the edge is more than 1 cm from the os
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
Suspected or confirmed placenta accreta spectrum (PAS)
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 ≥34 weeks with ongoing bleeding, or at any gestational age with uncontrolled hemorrhage, maternal instability, or nonreassuring fetal status: cesarean delivery without delaying for corticosteroids; if bleeding stops and mother and fetus are stable, plan cesarean at 36 0/7-37 6/7 weeks
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 sharply raises placenta accreta spectrum risk (~11% with one prior cesarean, ~40-67% with two or more) — evaluate for PAS with expert ultrasound (± MRI) and plan delivery at a PAS-capable center; cesarean hysterectomy at 34 0/7-35 6/7 weeks only if PAS is suspected, otherwise cesarean at 36 0/7-37 6/7 weeks.
Cesarean delivery is mandatory when the placenta covers the internal os; a low-lying placenta with its edge 1-2 cm from the os in late pregnancy may be offered a trial of labor (most deliver vaginally), while an edge within 1 cm carries a much higher cesarean rate.
Painless bright red bleeding is classic for previa; painful dark bleeding with uterine tenderness suggests abruption.
References
ACOG CO 831 — ACOG Committee Opinion No. 831: Medically Indicated Late-Preterm and Early-Term Deliveries (Obstet Gynecol 2021;138(1):e35-e39)
ACOG/SMFM OCC 7 (2018) — ACOG/SMFM Obstetric Care Consensus No. 7: Placenta Accreta Spectrum (Obstet Gynecol 2018;132(6):e259-e275; also Am J Obstet Gynecol 2018;219(6):B2-B16)
SMFM Consult #44 (2018) — Society for Maternal-Fetal Medicine Consult Series #44: Management of Bleeding in the Late Preterm Period (Am J Obstet Gynecol 2018;218(1):B2-B8)
Silver 2006 — Silver RM et al. Maternal Morbidity Associated With Multiple Repeat Cesarean Deliveries (Obstet Gynecol 2006;107(6):1226-1232)
Jansen 2019 — Jansen CHJR et al. Vaginal Delivery in Women With a Low-Lying Placenta: A Systematic Review and Meta-Analysis (BJOG 2019;126(9):1118-1126)
Fetal Imaging Workshop 2014 — Reddy UM et al. Fetal Imaging: Executive Summary of a Joint NICHD, SMFM, AIUM, ACOG, ACR, SPR, and SRU Fetal Imaging Workshop (Obstet Gynecol 2014;123(5):1070-1082)
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