11/14/24, 10\:50 AM Placenta Praevia

Placenta Praevia

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Placenta praevia\: cause of antepartum haemorrhage (bleeding > 24 weeks gestation) where the placenta overlies the
lower uterine segment.
Incidence\: 5% have low-lying placenta at 20-week scan, 0.5% at delivery; overall incidence 1/200 births.
Aetiology\: exact cause unknown, may include abnormal endometrial vascularisation due to atrophy, scarring from surgery,
trauma, or infection.
Grades\:
Grade 1\: low-lying, not covering internal os.
Grade 2\: marginal, reaching internal os.
Grade 3\: partial, partially covering internal os.
Grade 4\: complete, covering internal os.
Risk factors\:
Previous placenta praevia
Previous caesarean section (risk increases with the number of CS)
Advanced maternal age
Increased parity
Smoking, cocaine use during pregnancy
Previous spontaneous or induced abortion
De
Assisted conception (IVF)
Clinical features\:
Most cases asymptomatic, detected at 20-week scan.
History\: painless bright red vaginal bleeding (>24 weeks), light contractions, assess fetal movements, obstetric history,
medical history (endometriosis), assisted conception (IVF), smoking/drug use, post-coital bleeding.
Examination\: no digital vaginal exam (risk of heavy bleeding), speculum exam to check membranes and cervix.
Typical
Di
Placental abruption\: painful, dark red bleeding, may be concealed,
'woody' or 'tense' uterus.
Uterine rupture\: usually during labour, with a history of caesarean section.
Vasa praevia\: fetal blood vessels near internal os, triad of vaginal bleeding, rupture of membranes, fetal deterioration.
Benign lesions (e.g., cervical ectropion), malignant lesions (e.g., carcinoma), infections (e.g., chlamydia).
Investigations\:
Bedside\: CTG in women >26 weeks gestation.
Laboratory\: FBC, U&Es, LFTs (rule out hypertensive conditions), group and save/crossmatch (possible transfusion), clotting
pro
Imaging\: transvaginal ultrasound for de
Management\:
Asymptomatic\: rescan at 32 or 36 weeks, serial scans every two weeks if still present,
delivery method determination (elective caesarean at 38 weeks for major placenta praevia; trial of vaginal delivery if minor
and placenta >2 cm from internal os).
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With bleeding (antepartum haemorrhage)\: rapid ABCDE assessment, resuscitation, emergency caesarean if unable to
stabilise or in labour.
Complications\:
Maternal\: haemorrhage (trauma, cervical opening, abruption risk), hypovolemic shock, rare death (postpartum
haemorrhage major cause).
Fetal\: haemorrhage, intrauterine growth restriction (IUGR), premature birth.
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A comprehensive topic overview

Introduction

Placenta praevia is a cause of antepartum haemorrhage (de
placenta overlies the lower uterine segment.
Five percent of women have a low-lying placenta at their 20-week scan, but only 0.5% at delivery because the placenta
migrates during pregnancy.
The incidence of placenta praevia is rising due to increasing caesarean section and assisted reproduction (IVF) rates, it has
an overall incidence of 1/200 births.
1

Aetiology

The exact cause of placenta previa is unknown. Potential causes include abnormal vascularisation of the endometrium due
to atrophy or scarring from previous surgery, trauma, or infection.
Grades of placenta praevia
There are four grades of placenta praevia\:
Grade 1 (minor)\: placenta does not cover internal cervical os but is low lying
Grade 2 (marginal)\: lower edge reaching the internal os
Grade 3 (partial)\: lower edge partially covering the internal cervical os
Grade 4 (complete)\: lies over the internal cervical os

Risk factors

Risk factors for placenta praevia include\:
3
Previous history of placenta praevia
Previous caesarean section (CS)\: one CS increases risk by 2.2, two CS by 4.1 and three CS by 22.4
Increasing maternal age
Increasing parity
Smoking
Cocaine use during pregnancy
Previous spontaneous or induced abortion
De
Assisted conception (IVF)

Clinical features

Most cases of placenta praevia are asymptomatic and are detected on routine ultrasound at the 20-week scan.
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History
Typical symptoms of placenta praevia include\:
Antepartum haemorrhage\: painless bright red vaginal bleeding (>24 weeks gestation)
Light contractions may be present
Other important areas to cover in the history\:
Fetal movements
Obstetric history\: previous pregnancies, delivery mode, gestation and complications (previous caesarean sections
increase risk)
Past medical history\: endometriosis
Assisted contraception (IVF)
Risk factors (e.g. smoking and drug use)
Provoking factors\: post-coital
Clinical examination
A digital vaginal examination should not be performed, as this may trigger heavy bleeding in uncon
praevia.
A careful speculum examination can be performed to check that membranes have not ruptured and that the cervix is
closed.
Typical clinical
Non-tender uterus
Vaginal bleeding
Signs of shock (pallor, distress, capillary re

Di

Possible di
Placental abruption\: usually painful, dark red blood, bleeding may be concealed. The uterus may feel 'woody' or 'tense'
on examination.
Uterine rupture\: usually occurs in labour with a history of previous caesarean section
Vasa praevia\: where fetal blood vessels run near the internal cervical os (associated with the characteristic triad of
vaginal bleeding, rupture of membranes and fetal deterioration).
Benign lesions (e.g. cervical ectropion – common)
Malignant lesions (e.g. carcinoma)
Infections (e.g. chlamydia)
For more information on other causes of antepartum haemorrhage, see the Geeky Medics guide to antepartum
haemorrhage.

Investigations

Bedside investigations
Relevant bedside investigations include\:
Cardiotocograph (CTG)\: in women above 26 weeks gestation
Laboratory investigations
Relevant laboratory investigations for placenta praevia include\:
FBC, U&Es, LFTs\: useful to rule out hypertensive conditions such as HELLP or pre-eclampsia
Group and save/crossmatch\: if large volumes of blood loss patient may require transfusion
Clotting pro\: important in the context of bleeding
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Kleihauer test\: required if the woman is resus negative
Imaging
Ultrasound is used to establish a de
The Royal College of Obstetricians and Gynaecologists (RCOG) recommend the use of transvaginal ultrasound as it
improves the accuracy of placental localisation and is considered safe.

Management

Asymptomatic placenta praevia
If a low-lying placenta is seen at the 20-week scan and the patient is asymptomatic, the patient should be rescanned at 32
or 36 weeks depending on whether placenta praevia is major or minor.
If placenta praevia is still present at the following scan, serial scans should be performed every two weeks from that point
onward.
A
Elective caesarean section for major placenta praevia at 38 weeks.
If minor, then a trial of vaginal delivery may be o
away from the internal os for attempted vaginal delivery.
Placenta praevia carries an increased risk of obstetric haemorrhage and hysterectomy. All women with placenta praevia
and their partners should have a discussion regarding complications and mode of delivery. Any decisions to decline blood
or blood products should be discussed openly and documented.
Placenta praevia with bleeding (antepartum haemorrhage)
Management of an antepartum haemorrhage due to placenta praevia includes a rapid ABCDE assessment and
resuscitation. Maternal resuscitation should not be delayed to determine fetal viability.
If the patient is unable to be stabilised or is in labour an emergency caesarean section is recommended.

Complications

Maternal complications of placenta praevia include\:
Haemorrhage\: bleeding can occur from simple trauma (e.g. intercourse) or as the cervix opens during labour due to the
low-lying placenta. Additionally, there is a risk of abruption when the fetus moves into the lower uterine segment.
Hypovolemic shock secondary to bleeding
Death is rare (a major cause of death in women with placenta praevia is now postpartum haemorrhage)
Fetal complications of placenta praevia include\:
Fetal haemorrhage
Intrauterine growth restriction (IUGR)
Premature birth

References

Neilson JP. I n t e r v e n t i o n s f o r s u s p e c t e d p l a c e n t a p r a e v i a . Cochrane Database Systematic Review. 2003(2)\:CD001998.
OpenStax College. P l a c e n t a P r a v e i a . Licence\: [CC BY 3.0]
Faiz AS, Ananth CV. Etiology and risk factors for placenta praevia\: an overview and meta-analysis of observational studies.
Journal of Maternal, Fetal and Neonatal Medicine. 2003 Mar13(3)\:175-90
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Reviewer

Dr Rachel Greenwood
Obstetrics & Gynaecology Registrar

Related notes

Amniotic Fluid Embolism
Antenatal Screening for Down’s Syndrome
Antepartum Haemorrhage (APH)
Breech Presentation
Caesarean Section

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Contents

Introduction
Aetiology
Risk factors
Clinical features
Di
Investigations
Source\: geekymedics.com
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