Placenta Previa:

Causes, Diagnosis,
and Management
Makarenko Viktoriia
Student
Bukovinian State Medical
University

Abstract
Placenta previa is a pregnancy
complication characterized by
the abnormal implantation of the
placenta over or near the cervical
os. It occurs in approximately 1
in 200 pregnancies and is a
leading cause of third-trimester
bleeding. Risk factors include
previous cesarean sections,
multiparity, and assisted
reproductive technology.
Diagnosis is primarily made via
ultrasound, and management
depends on gestational age,
bleeding severity, and fetal well-
being. This article explores the
pathophysiology, risk factors,
clinical presentation, diagnosis,
management, and potential
complications of placenta previa.

1. Introduction
Placenta previa is a significant
obstetric condition that can lead
to severe maternal and fetal
complications, including
hemorrhage, preterm birth, and
the need for cesarean delivery. It
occurs when the placenta
partially or completely covers the
cervix, preventing normal vaginal
delivery. Advances in prenatal
imaging have improved early
diagnosis, allowing for better risk
stratification and management.
This article provides an in-depth
review of placenta previa,
emphasizing its clinical
importance and strategies for
optimizing maternal and fetal
outcomes.
2. Pathophysiology
and Classification
Placenta previa results from
abnormal placental implantation
within the lower uterine segment.
The exact mechanism is not fully
understood, but it is thought to
be associated with defective
decidualization, leading to
improper placental attachment.

2.1 Types of Placenta

Previa
Placenta previa is classified
 based on the degree of cervical
os coverage:

Ÿ Complete Placenta Previa –

The placenta entirely covers the
cervical opening.

Ÿ Partial Placenta Previa – The

placenta
Ÿ partially covers the cervix.

Ÿ Marginal Placenta Previa – The

edge of the placenta extends to
the cervix but does not cover it.

Ÿ Low-lying Placenta – The

placenta is implanted in the lower
uterine segment but does not
reach the cervix; it may resolve
as the uterus expands.

As the pregnancy progresses,

some cases of placenta previa,
especially marginal or low-lying
types, may resolve due to
placental migration caused by
uterine growth.
3. Risk Factors
Several maternal and obstetric
factors increase the risk of
placenta previa:
Ÿ Previous Cesarean Section –
Each prior C-section increases
the risk due to uterine scarring.

Ÿ Multiparity – A higher number of

pregnancies raises the likelihood
of abnormal placental
implantation.

Ÿ Advanced Maternal Age –

Women over 35 years have a
higher risk.

Ÿ History of Placenta Previa – A

previous diagnosis significantly
raises recurrence risk.

Ÿ Multiple Gestations – More

placentas and a larger placental
 surface area increase the risk.

Ÿ Assisted Reproductive
Technology (ART) – In vitro
fertilization (IVF) is associated
with a higher incidence.
Ÿ Uterine Surgery or Scarring –
Previous myomectomy or
endometrial damage contributes
to abnormal placentation.

Ÿ Smoking and Substance Use –

These factors are linked to
vascular abnormalities affecting
placental implantation.

4. Clinical
Presentation
The hallmark symptom of
placenta previa is painless,
bright red vaginal bleeding in
the second or third trimester,
 often occurring after 20 weeks of
gestation. The bleeding may be
episodic, spontaneous, and
recurrent, often increasing in
severity as pregnancy
progresses. Other clinical
features include:

Ÿ Absence of Abdominal Pain –

Unlike
Ÿ placental abruption, placenta
previa does not typically cause
uterine tenderness.

Ÿ Non-reassuring Fetal Heart

Rate Patterns – In cases of
significant hemorrhage, fetal
distress may occur.

Ÿ Malpresentation (e.g., breech

or transverse lie) – The
abnormal placental location can
affect fetal positioning.

Any suspected case of placenta

previa warrants immediate
evaluation to prevent
complications.
5. Diagnosis
5.1 Imaging Studies
 Ultrasound is the gold standard
for diagnosing placenta previa:

Ÿ Transabdominal Ultrasound
(TAS) – Often the initial
screening method but may be
limited by fetal position or
bladder fullness.

Ÿ Transvaginal Ultrasound
(TVUS) – Provides more precise
localization of the placenta and is
safe when performed by
experienced clinicians.

5.2 Magnetic
Resonance Imaging
(MRI)
MRI is occasionally used when
placenta accreta spectrum
disorders (placenta accreta,
increta, or percreta) are
suspected, particularly in patients
with prior uterine surgery.
 5.3 Clinical
Considerations
Ÿ Digital cervical examinations
should be avoided in suspected
placenta previa due to the risk of
triggering severe hemorrhage.

Ÿ Repeat ultrasounds at 32–36

weeks are recommended to
assess placental migration and
plan delivery accordingly.

6. Management of
Placenta Previa
The approach to management
depends on gestational age,
bleeding severity, and maternal
and fetal stability.

6.1 Expectant
Management
(Conservative
Approach)
 For stable patients with minimal
or no bleeding, outpatient
monitoring may be considered.
Key components include:

Ÿ Pelvic rest – Avoidance of

sexual intercourse and digital
cervical exams.

Ÿ Activity restriction – Limited

physical exertion to reduce
bleeding risk.

Ÿ Serial ultrasounds – To monitor

placental position and fetal
growth.
Ÿ Corticosteroids –
Recommended before 34 weeks
to enhance fetal lung maturity in
case of preterm birth.

6.2 Hospitalization for

Active Bleeding
Ÿ Patients with significant or
recurrent
Ÿ bleeding require hospitalization
for close monitoring.

Ÿ Intravenous fluids and blood

transfusions may be necessary
to manage maternal
hemodynamics.

Ÿ Fetal monitoring is essential to

detect distress or compromise.

Ÿ Tocolytics (e.g., nifedipine)

may be used short-term to delay
preterm labor in select cases.

6.3 Timing and Mode of

Delivery
Ÿ Elective Cesarean Section (C-
section): Recommended at 36–
37 weeks for complete or partial
previa, even in the absence of
bleeding.

Ÿ Emergency C-section:
Indicated in
Ÿ cases of massive hemorrhage or
fetal distress.

Ÿ Trial of Labor: Only considered

for marginal or low-lying placenta
if no significant bleeding is
present.

7. Complications of
Placenta Previa
7.1 Maternal
Complications
Ÿ Severe Hemorrhage – Can lead
to hypovolemic shock and
require blood transfusions.
Ÿ Placenta Accreta Spectrum –
Abnormal placental adherence,
often necessitating hysterectomy.

Ÿ Increased Risk of Postpartum

Ÿ Hemorrhage (PPH) – Due to
poor uterine contraction at the
site of placental implantation.

7.2 Fetal Complications

Ÿ Preterm Birth – Common due to
iatrogenic or spontaneous
preterm delivery.

Ÿ Fetal Growth Restriction (FGR)

– Reduced placental perfusion
may impact fetal growth.

Ÿ Neonatal Morbidity –
Respiratory distress syndrome,
anemia, and low birth weight are
possible outcomes.
8. Conclusion
Placenta previa is a serious
obstetric
condition requiring early
identification and careful
management to minimize
maternal and fetal risks.
Advances in ultrasound
technology have improved
diagnostic accuracy, allowing for
timely intervention. Management
strategies range from
conservative monitoring in stable
cases to planned cesarean
delivery for complete previa.
Multidisciplinary care involving
obstetricians, neonatologists,
and anesthesiologists is
essential for optimizing
pregnancy outcomes. Continued
research into the
pathophysiology and prevention
 of placenta previa will further
enhance maternal-fetal health.

References
Ÿ World Health Organization
(WHO). (2023). Management of
Placenta Previa: Clinical
Guidelines.
Ÿ American College of
Obstetricians and Gynecologists
(ACOG). (2022). Placenta Previa
and Placenta Accreta Spectrum.

Ÿ Royal College of Obstetricians

and Gynaecologists (RCOG).
(2021). Placenta Previa and
Vasa Previa: Diagnosis and
Management.

Ÿ Silver, R. M. (2020). Placenta

Accreta Spectrum:
Pathophysiology and Risk
Factors. Obstetrics &
Gynecology.

Ÿ Jauniaux, E., et al. (2019).

Prenatal Diagnosis and
Management of Placenta Previa.
The Lancet.