A nurse in a prenatal clinic is caring for a client who is at 38 weeks of gestation and reports heavy, red vaginal bleeding. The bleeding started spontaneously in the morning and is not accompanied by contractions. The client is not in distress and she states that she can "feel the baby moving." An ultrasound is scheduled stat. The nurse should explain to the client that the purpose of the ultrasound is to determine which of the following?

A. The biparietal diameter is used to estimate fetal size and gestational age, but it does not address the acute concern of vaginal bleeding. B. The primary purpose of a stat ultrasound in this scenario is to determine the location of the placenta. Painless, bright red bleeding at term is characteristic of placenta previa, and knowing the placental location is crucial for planning safe delivery. C. Fetal lung maturity is assessed via amniotic fluid tests and is not the immediate concern during active bleeding at term. D. Viability is typically determined early in pregnancy; at 38 weeks, fetal viability is assumed, and the focus is on maternal and fetal safety related to the bleeding.