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Placenta previa (mechanism of disease)

This is a flowchart on placenta previa, covering the etiology, pathophysiology, and manifestations. ADDITIONAL TAGS: Risk factors / SDOH Cell / tissue damage Structural factors Placenta previa Medicine / iatrogenic Infectious / microbial Biochem / metabolic Immunology / inflammation Signs / symptoms Tests / imaging / labs Environmental / toxin Reproductive physiology Growth / neoplastic Pathophysiology Etiology Manifestations Endometrial damage in lower uterine segment Uterine scarring creates environment that is rich in oxygen and collagen Implantation of a zygote (fertilized egg) in rich environment Outer layer of dividing zygote (blastocyst), made of trophoblast cells, develops into placenta Placenta previa: placenta either partially or completely covers the internal os Placenta grows toward ↑ blood supply of uterine fundus (while the other side atrophies) → migration Sudden, painless, bright red vaginal bleeding Usually in the third trimester, before rupture of membranes +/- recurrent bleeding episodes, self-limited; re- occurs during onset of labor Soft, nontender uterus Usually no fetal distress Since blood loss is maternal In contrast to placental abruption Severe hemorrhage → shock: Hypotension Tachycardia Previous suction Previous cesarean delivery Previous / recurrent abortions Maternal age 35 years Multiparity Short interval between pregnancies Previous placenta previa Risk factors: Previous curettage Assisted reproductive technology Management: Lower segment c section is preferred; only attempt vaginal delivery if stable mother, reassuring fetal status, in operating room In antepartum hemorrhage, avoid digital vaginal exam Transvaginal or transabdominal ultrasound, as part of routine prenatal care, assesses placental position