26/03 Notes on Placenta Previa and Related Conditions

Patient Decision-Making and Ethical Considerations

• A case involving a young Jehovah's Witness woman who needed a blood transfusion due to placenta separation.

• Tension existed between the patient’s beliefs (regarding blood transfusion) and her medical needs.

• Quick decision-making was crucial as fetal heart rate was not detectable.

• The patient opted for the blood transfusion during surgery, prioritizing her survival and future pregnancies.

Understanding Placenta Previa

• Definition: A condition where the placenta is abnormally positioned in the lower part of the uterus.

• Classification based on position relative to the cervix:

• Low-lying placenta: Within 2 cm of the cervix, but not covering it.

• Complete previa: Placenta entirely covering the cervical opening.

• Partial previa: Placenta partially covering the cervical opening.

Types of Placenta Previa

• Placenta Accreta: Abnormal attachment to the uterine wall, occurring in 0.3% to 0.5% of pregnancies. Increased risk after multiple C-sections.

• Placenta Increta: Penetration into the uterus to the muscle layer.

• Placenta Percreta: Growth through the muscle and invades surrounding organs (bladder, rectum).

Risk Factors for Placenta Previa

• Previous uterine surgeries (e.g., terminations, removals).

• Presence of uterine fibroids.

• Multiple pregnancies (multiparity).

• Advanced maternal age.

• Smoking and substance abuse affecting the uterus.

Pathophysiology of Placenta Previa

• The placenta's abnormal location is due to potential damage to the endometrial lining, limiting implantation options.

• History of uterine surgery can lead to scarring, causing lower uterine placements.

Development and Function of the Placenta

• The embryo is surrounded by chorionic villi that contribute to the formation of the placenta.

• The placenta's role includes providing oxygen and nutrients to the developing fetus.

Clinical Considerations and Management

• Importance of ultrasound assessment to evaluate the placement of the placenta.

• Monitoring for complications during labor, especially with previa cases, since it may lead to severe bleeding.

Vasa Previa

• A rare condition where fetal blood vessels cross or run near the internal cervical os.

• Can be dangerous if vessels rupture during labor, leading to fetal hemorrhage.

Implications for Future Pregnancies

• Women with high parity, history of previa, or significant uterine surgery should be monitored closely in subsequent pregnancies for recurrence risk.

• Counseling regarding potential complications and delivery options must be proactively discussed.

Postpartum Considerations

• Placenta examination after delivery can reveal significant findings (e.g., thrombosis) that inform future pregnancy management strategies.

Antepartum Haemorrhage:

• Abnormal placentas can be a reason for antepartum hemorrhage.

Placenta Praevia:

• Defined as a placenta overlying the cervical opening, causing potential complications.

Risk Factors:

• Previous uterine surgeries (e.g., terminations, removals).

• Presence of uterine fibroids.

• Multiple pregnancies (multiparity).

• Advanced maternal age.

• Smoking and substance abuse affecting the uterus.

Placental Implantation and Development:

• The embryo is surrounded by chorionic villi that contribute to the formation of the placenta, crucial for supplying oxygen and nutrients to the developing fetus.

Implantation and Development (again):

• The abnormal location of the placenta can be due to potential damage to the endometrial lining, leading to difficulties in implantation.

Praevia Pathophysiology:

• Low-lying is different than previa; low-lying placenta is within 2 cm of the cervix but does not cover it, whereas previa covers the cervical opening.

Vasa Praevia:

• A rare condition where fetal blood vessels cross or run near the internal cervical os, posing risks if vessels rupture during labor, leading to fetal hemorrhage.

Placenta Accreta:

• Abnormal attachment to the uterine wall, occurring in 0.3% to 0.5% of pregnancies, and associated with previous C-sections.

Normal Placenta vs. Placenta Accreta Spectrum (PAS):

• Normal placenta allows for appropriate implantation and development, while placenta accreta reflects abnormal attachment, posing significant risks for maternal and fetal health.