Placenta Previa

Definition | Aetiology | Risk Factors | Signs and Symptoms | Management | References

Definition

Placenta Previa is a condition in pregnancy where the placenta implants in the lower part of the uterus and covers part or all of the internal cervical os. This can cause significant maternal and fetal morbidity and mortality due to the risk of severe bleeding (antepartum haemorrhage) as the cervix dilates.

Aetiology

The exact cause of placenta previa is unknown, but several factors increase the likelihood of its occurrence:

• Previous Placenta Previa: Having a history of placenta previa in a previous pregnancy significantly increases the risk.
• Multiple Pregnancies: A higher number of previous pregnancies or births increases the risk.
• Advanced Maternal Age: Women over the age of 35 are at a higher risk.
• Uterine Surgery: Previous surgeries such as caesarean sections or myomectomy increase the risk.
• Multiparity: The more pregnancies a woman has had, the higher the risk.
• Smoking: Tobacco use during pregnancy is associated with an increased risk of placenta previa.

Risk Factors

• Previous placenta previa.
• Advanced maternal age (over 35 years).
• Multiple pregnancies (high parity).
• Previous caesarean section or other uterine surgery.
• Smoking during pregnancy.
• Multiple gestation (e.g., twins, triplets).

Signs and Symptoms

Placenta previa often presents with painless vaginal bleeding in the second or third trimester. Other signs and symptoms include:

• Painless Vaginal Bleeding: The hallmark symptom, typically occurring after 20 weeks of gestation.
• Abnormal Fetal Position: Breech or transverse lie is common due to the lower uterine segment being occupied by the placenta.
• Soft, Non-Tender Uterus: The uterus remains soft and non-tender even with significant bleeding.

Be aware that vaginal examination is contraindicated in women with suspected placenta previa due to the risk of causing severe bleeding.

Management

Management of placenta previa depends on the gestational age, severity of bleeding, and maternal and fetal condition:

• Expectant Management:
  • Used in cases of mild bleeding and preterm pregnancy. Involves close monitoring with bed rest, avoiding vaginal intercourse, and corticosteroid administration to enhance fetal lung maturity if preterm delivery is anticipated.
  • Serial ultrasounds may be performed to monitor the position of the placenta, as it may migrate away from the cervix as the pregnancy progresses.
• Active Management:
  • Hospitalisation: In cases of heavy or recurrent bleeding, hospital admission is required for maternal and fetal monitoring.
  • Delivery Planning:
    • Elective caesarean section is typically planned for 36-37 weeks of gestation if the placenta previa persists.
    • Emergency caesarean section may be necessary if there is severe bleeding or signs of fetal distress.
  • Blood Transfusion: May be required in cases of significant maternal blood loss.
• Avoidance of Vaginal Examination: Vaginal examinations are avoided to prevent triggering haemorrhage.
• Consultation and Referral: Early consultation with an obstetrician is essential for all cases of suspected placenta previa.

References

1. NHS (2024) Placenta Previa. Available at: https://www.nhs.uk/conditions/placenta-previa/ (Accessed: 24 June 2024).
2. National Institute for Health and Care Excellence (2024) Placenta Previa: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng121 (Accessed: 24 June 2024).
3. Royal College of Obstetricians and Gynaecologists (2024) Green-top Guideline No. 27: Placenta Previa and Placenta Accreta. Available at: https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg27/ (Accessed: 24 June 2024).

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