Up to one-fifth of parturients may experience vaginal bleeding. Bleeding is more common in the first trimester. Causes may be clinically minor. But when due to more serious causes such as placental previa, uterine rupture, or placental abruption, outcomes may be fatal to the fetus and the mother. It is important to be able to delineate the different etiologies and understand the anesthetic management for these patients.
Placenta previa occurs when the placenta implants in the lower portion of the uterus. It occurs in approximately in 0.5% of pregnancies. There are three degrees of placenta previa (Figure 167-1). Total placenta previa occurs when the placenta covers the entire cervical os. Partial placenta previa is when the placenta covers a portion of the cervical os. Lastly, marginal placenta previa happens when the placenta is next to the cervical os and does not cover the os.
Degrees of placenta previa. (Reproduced with permission from DeCherney AH, Nathan L, Laufer N, Roman AS, eds. Current Diagnosis & Treatment: Obstetrics & Gynecology. 11th ed. New York, NY: McGraw-Hill Education, Inc.; 2013: Fig. 18-1 A–C.)
The reason why placental previa occurs is unknown. There are several risk factors associated with placental previa. These include previous uterine surgery including cesarean delivery, previous placental previa, large placenta, multiparity, and advanced maternal age. Previa is often associated with vaginal bleeding that is painless, usually in the second or third trimester of pregnancy. The initial bleeding usually starts and ends spontaneously. If the fetus is preterm, treatment involves bed rest and observation.
Diagnosis should be confirmed by ultrasound. The main concern is severe hemorrhage for the parturient. It is also possible for the blood loss to impact the fetus. Concerns for the fetus also include preterm delivery or uteroplacental insufficiency.
Patients should have adequate vascular access. Labs including a complete blood count and type and cross should be performed. Cesarean delivery is required for most previa deliveries. It is only possible to avoid cesarean delivery when there is marginal placental previa and the placenta is more than 2 cm from the cervical os. Cesarean is planned when there is active labor or significant bleeding. When possible, delivery is delayed to wait until the fetus is mature as possible and after steroids have been given to enhance fetal lung development.
When a parturient with placenta previa is stable and undergoing cesarean delivery, neuraxial anesthesia is preferred but not mandatory. Because there is significant risk of bleeding, the patient should have two large peripheral intravenous catheters. Use of an arterial line should be considered when appropriate. Most anesthesiologists also have the patient typed and crossmatched with at least two units of packed red blood cells ready.