Final answer:
An echogenic mass is often located at or near the placental end of the umbilical cord, a structure that is part of the vital connection between mother and fetus for nutrient and waste exchange. The correct option is 1) The placental end of the cord.
Step-by-step explanation:
An echogenic mass in the context of fetal ultrasound usually refers to a structure within the uterus that reflects sound waves more than the surrounding tissues. While specific location of the echogenic mass could vary, when considering the umbilical cord, the mass is often at or near the placental end of the cord.
The placenta is a critical structure that forms the interface between the mother and the fetus, with the maternal portion developing from the endometrium and the fetal portion including the chorionic villi and umbilical cord, which contains two arteries and a vein allowing for the exchange of nutrients and waste between the mother and fetus.