Five to 10 percent of women have vaginal bleeding in late pregnancy. The clinician must distinguish between placental causes (placenta previa, placental abruption, vasa previa) and nonplacental causes (labor, infection, disorders of the lower genital tract, systemic disease) (eFigures 19–8 and 19–9). The approach to bleeding in late pregnancy depends on the underlying cause, the gestational age at presentation, the degree of blood loss, and the overall status of the mother and her fetus. The cause of antepartum bleeding after midpregnancy is unknown in one-third of cases.
Placenta previa. A: Partial. B: Complete. (Reproduced, with permission, from Benson RC. Handbook of Obstetrics & Gynecology, 8th ed. Originally published by Lange Medical Publications. Copyright © 1983 by The McGraw-Hill Companies, Inc.)
Spectrum of placental abruption. Sym, symphysis. (Redrawn and reproduced with permission from Beck and Rosenthal. Obstetrical Practice, 7th ed. Williams & Wilkins, 1957.)
The patient should initially be observed closely with continuous fetal monitoring to assess for fetal distress. A complete blood count with platelets and a prothrombin time (INR) should be obtained and repeated serially if the bleeding continues. If hemorrhage is significant or if there is evidence of acute hypovolemia, the need for transfusion should be anticipated and an appropriate volume of red cells prepared with cross-matching. Ultrasound examination should be performed to determine placental location (eFigure 19–10 and 19–11). Digital pelvic examinations are done only after ultrasound examination has ruled out placenta previa. Administration of anti-D immune globulin may be required for women who are Rh negative.
Total placenta previa. Sagittal midline sonogram in the last trimester shows the placenta (P) completely covering the internal cervical os (arrowhead). F, fetus. (Reproduced, with permission, from Krebs CA, Giyanani VL, Eisenberg RL. Ultrasound Atlas of Disease Processes. Originally published by Appleton & Lange. Copyright © 1993 by The McGraw-Hill Companies, Inc.)
Placenta previa. Sagittal sonogram of the lower uterine segment in a patient with vaginal bleeding. The placenta (P) is seen to encroach upon the cervix (arrows) consistent with a marginal placenta previa. (Courtesy of Peter W. Callen, MD.)
Placenta previa occurs when the placenta implants over the internal cervical os. Risk factors for this condition include previous cesarean delivery, increasing maternal age, multiparity, and smoking. If the diagnosis is initially made in the first or second trimester, the ultrasound ...