What are the risks presented to the mother and the fetus from placenta previa?
When is expectant management acceptable?
What are the evidence-based recommendations for the management of placenta previa?
When is delivery indicated in these cases?
A 31-y.o. nulliparous woman at 35 weeks gestation presents with complaints of painless, bright red vaginal bleeding. She is concerned about the well-being of her fetus, as this pregnancy was conceived by IVF. You confirm a complete placenta previa on transabdominal ultrasonography.
Placenta previa is defined as a placenta covering the internal cervical os. The incidence is estimated to range from 1 in 200 to 1 in 250 pregnancies at term, but it varies worldwide.1,2 Risk factors include advanced maternal age, multiparity, multifetal gestation, male fetal gender, prior cesarean delivery, previous spontaneous and elective pregnancy terminations, previous uterine surgery, maternal tobacco or cocaine use, and use of assisted reproductive technology.1-4 There is also a direct correlation between the number of previous cesarean deliveries and risk for placenta previa.
Placenta previa is associated with numerous adverse maternal outcomes, owing to a ten-fold increased risk of antepartum vaginal bleeding, and subsequently the increased need for blood transfusion, peripartum hysterectomy, intensive care unit (ICU) admission, sepsis, thrombosis, and even death.1 The presence of one or more prior cesarean deliveries further increases these risks.5
Fetal complications are primarily attributable to preterm delivery. The average gestational age at delivery among women with previa is 35 weeks, with approximately half of all women delivering at ≤37 weeks gestation.1,5 The risk of neonatal mortality appears to be threefold to fourfold higher compared to neonates born to women without placenta previa,6 while long-term outcomes do not differ.7
The classic presentation of a patient with placenta previa is one with painless vaginal bleeding. However, the presence of pain should not reduce the clinician’s suspicion for previa. In developed countries, the majority of placenta previas are diagnosed during midtrimester ultrasound (Figure 43-1). In cases of suspected placenta previa on transabdominal ultrasound, the use of transvaginal ultrasound can and should be employed, as it has greater diagnostic accuracy. Theoretical concerns for increased risk of bleeding with the use of transvaginal ultrasonography largely have been disproven.8 Translabial ultrasonography is another, more accurate alternative to transabdominal imaging.1
Placenta previa on transabdominal ultrasound. (Reproduced with permission from Fleischer AC, Abramowicz JS, Gonçalves LF, et al: Fleischer’s Sonography in Obstetrics and Gynecology: Textbook and Teaching Cases, 8th ed. New York, NY: McGraw-Hill Education, Inc; 2018).