Placenta Praevia

PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

Antepartum haemorrhage is defined as any vaginal bleeding from the 24th week of gestation until delivery, although 20-28 weeks of gestation have also been cited.[1] It is an important cause of maternal and fetal morbidity and mortality. The most important causes are placenta praevia and placental abruption which are more than half the cases.[2]

Placenta praevia exists when the placenta is inserted wholly or in part into the lower segment of the uterus.

Placenta praevia is graded as: I - encroaches the lower segment but does not reach the cervical os. II - reaches the internal cervical os but does not cover it. III - covers part of the cervical os. IV - completely covers the os, even when the cervix is dilated.

Numbers of incidents are rising with the increasing Caesarean section rate. The overall incidence is 1/200 births, and 1/1,000 are grade IV with placenta over the entire cervix.[3]

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Risk factors[4]

  • Previous history of placenta praevia.
  • Advancing maternal age.
  • Increasing parity.
  • Smoking.
  • Cocaine use.
  • Previous Caesarean section.
  • Previous spontaneous or induced abortion.
  • It may be an incidental finding on routine ultrasound.
  • Painless bleeding starting after the 28th week (although spotting may occur earlier) is usually the main sign:
    • Typically, it is sudden and profuse but usually does not last for long and so is only rarely life-threatening.
    • Women with placenta praevia are reported to be 14 times more likely to bleed in the antenatal period compared with women without placenta praevia.[4]
  • There may be some initial pain in approximately 10% of cases with co-incidental placental abruption.
  • In 25% of cases, spontaneous labour appears in the subsequent few days.
  • In a small proportion of cases, less dramatic bleeding occurs or does not start until spontaneous rupture of membranes or onset of labour.
  • The uterus is often normal on palpation. It may be impossible to push the high presenting part into the pelvic inlet.
  • In 15% of cases the fetus presents in an oblique or transverse lie.
  • Usually, there is no indication of fetal distress unless complications occur.

Clinical suspicion should be high in any woman with vaginal bleeding after 20 weeks of gestation. A high presenting part, an abnormal lie and painless or provoked bleeding, irrespective of previous imaging results, are more suggestive of a low-lying placenta but may not be present. The definitive diagnosis usually relies on ultrasound imaging:[5]

  • Ultrasound:
    • The diagnosis is by ultrasound imaging determining the site of the leading edge of the placenta.
    • This may be 'normally low' at the 20-week scan, but placental migration occurs during the second and third trimesters, as a result of the development of the lower uterine segment. Migration is less likely if the placenta is posterior or if there has been a previous Caesarean section.
    • Transvaginal scans improve the accuracy of placental localisation and are safe, so the suspected diagnosis of placenta praevia at 20 weeks of gestation by abdominal scan should be confirmed by transvaginal scan.[4]
    • It can be confused with a blood clot in the lower uterine segment.
  • Other investigations will depend on context but may include FBC, group and cross-match, fetal monitoring.

The following is a suggested policy for screening from the Royal College of Obstetricians and Gynaecologists' guideline:[5]

  • A further transvaginal scan is required for all women whose placenta reaches or overlaps the cervical os at their anomaly scan as follows (most low-lying placentas detected at a 20-week anomaly scan will resolve by the time the baby is born; therefore only a woman whose placenta extends over the internal cervical os should be offered another transabdominal scan):
    • Women who bleed should be managed individually according to their needs.
    • In cases of asymptomatic suspected minor praevia, follow-up imaging can be left until 36 weeks.
    • In cases with asymptomatic suspected major placenta praevia, a transvaginal ultrasound scan should be performed at 32 weeks, to clarify the diagnosis and allow planning for third-trimester management and delivery.
  • Grades I and II (minor) may be able to deliver vaginally; Grades III and IV (major) will require Caesarean section by the most experienced obstetrician and anaesthetist on duty. As a minimum requirement during a planned procedure, a consultant obstetrician and anaesthetist should be present within the delivery suite.[5]
  • Prior to delivery there should be discussions regarding delivery, haemorrhage, possible blood transfusion and major surgical interventions, such as hysterectomy.
  • Where possible, elective Caesarean section should be deferred to 38 weeks to minimise neonatal morbidity.
  • In response to the findings of the confidential enquiry a care bundle for placenta praevia has been developed with six elements of good care:[6] 
    • Consultant obstetrician planned and directly supervising delivery.
    • Consultant anaesthetist planned and directly supervising anaesthetic at delivery.
    • Blood and blood products available.
    • Multidisciplinary involvement in preoperative planning.
    • Discussion and consent including possible interventions, eg hysterectomy.
    • Locally available level 2 critical care bed.
  • Women with major placenta praevia who have previously bled should be admitted and managed as inpatients from 34 weeks of gestation.
  • Women with major placenta praevia who remain asymptomatic, having never bled, require careful counselling before contemplating outpatient care:
    • Any home-based care requires close proximity with the hospital, the constant presence of a companion and full informed consent from the woman.[5]
    • Any woman being managed at home should attend hospital immediately if she experiences any bleeding, any contractions or any pain (including vague suprapubic period-like aches).
  • The mode of delivery should be based on clinical judgement supplemented by ultrasound findings. A placental edge less than 2 cm from the internal os is likely to need delivery by Caesarean section, especially if it is posterior or thick.[5]
  • For preterm delivery when immediate delivery is not necessary, maternal steroids may be indicated in order to promote fetal lung development and reduce the risk of respiratory distress syndrome.

Acute bleeding

Admit the patient to hospital.

DO NOT PERFORM A VAGINAL EXAMINATION, as this may start torrential bleeding.

  • Blood loss is assessed and cross-matched for possible transfusion.
  • Prompt, adequate replacement of blood, crystalloids or fresh-frozen plasma through more than one intravenous line. It might be necessary to pump blood under pressure, with constant monitoring of the pulse rate and the arterial blood pressure.[7]
  • Oxytocin and prostaglandins can correct uterine atony.
  • Appropriate surgical intervention may be required:
    • Ligation of the uterine arteries, ovarian arteries and hypogastric arteries will usually control uterine bleeding, and arterial embolisation is also effective.
    • Hysterectomy should also be considered in severe cases.
  • In severe bleeding the baby is delivered urgently whatever its gestational age.
  • In less severe bleeding, where the fetus is at a gestational age less than 36 weeks, expectant therapy is appropriate with women remaining in hospital.
  • In many cases, pregnancy can continue to 36 weeks after which time the benefits of additional maturity need to be weighed against the risk of major haemorrhage and the possibility that repeated small haemorrhages may cause intrauterine growth restriction.
  • Labour can then be induced at an optimal time decided upon by tests of fetal lung maturity (including assessment of amniotic fluid, surfactants and ultrasound growth measurements).
  • Potentially fatal hypovolaemic shock resulting from severe antepartum, intrapartum or postpartum bleeding. Also, infection and embolism.
  • Rarely, placenta praevia accreta (placenta accreta is an abnormally firm attachment of the placenta to the uterine wall and the risk is increased in women with placenta praevia).[5]
  • Fetal haemorrhage, prematurity, intrauterine asphyxia or birth injury.
  • A higher rate of pregnancy complications, including abruption placenta, antepartum haemorrhage and intrauterine growth restriction, has been reported in women with low-lying placentas identified in the second trimester.[8][4]
  • The perinatal mortality rate associated with placenta previa ranges from 2-3%.
  • Maternal mortality secondary to haemorrhage is 0.39 per 100,000 maternities in the UK.[6] 

Further reading & references

  1. El-Mowafi D; Bleeding in Late Pregnancy (Antepartum Haemorrhage), Geneva Foundation for Medical Education and Research, 2008
  2. Sinha P, Kuruba N; Ante-partum haemorrhage: an update. J Obstet Gynaecol. 2008 May;28(4):377-81.
  3. Neilson JP; Interventions for suspected placenta praevia. Cochrane Database Syst Rev. 2003;(2):CD001998.
  4. Antenatal care; NICE Clinical Guideline (March 2008)
  5. Placenta Praevia, Placenta Praevia Accreta and Vasa Praevia: Diagnosis and Management; Royal College of Obstetricians and Gynaecologists (January 2011)
  6. Saving Mothers' Lives. Reviewing maternal deaths to make motherhood safer: 2006-2008; Centre for Maternal and Child Enquiries (CMACE), BJOG, Mar 2011
  7. Papp Z; Massive obstetric hemorrhage. J Perinat Med. 2003;31(5):408-14.
  8. Joy S et al, Placenta previa, eMedicine, Feb 2010

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Colin Tidy
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