Which of the following should the nurse identify as the correct number of vessels in the umbilical cord?

The placenta is a vital organ for fetal development, facilitating maternal-fetal exchange. It performs gas exchange, nutrient delivery, and waste removal between maternal and fetal blood without direct blood mixing. The placenta also transfers immunoglobulins, mainly immunoglobulin G (IgG), providing passive immunity to the fetus. It produces hormones essential for pregnancy maintenance but does not produce fetal hemoglobin or regulate fetal blood pressure directly. Normal placental weight ranges from 400 to 600 grams at term.

Rationale for correct answers

A. The placenta facilitates the transfer of oxygen from maternal blood to fetal blood via diffusion through the placental membrane, critical for fetal oxygenation.

B. It acts as an interface for the excretion of fetal waste products such as carbon dioxide and urea into maternal circulation for elimination.

C. The placenta transfers maternal immunoglobulins, especially IgG, across the syncytiotrophoblast to the fetal circulation, providing passive immunity.

Rationale for incorrect answers

D. Fetal hemoglobin (HbF) is synthesized by the fetal liver and bone marrow, not by the placenta.

E. Regulation of fetal blood pressure is controlled by fetal cardiovascular and renal systems, not directly by the placenta.

Take home points

• The placenta transfers oxygen and nutrients and removes fetal wastes.
• It mediates passive immunity by transferring maternal antibodies to the fetus.
• Placenta does not synthesize fetal hemoglobin or regulate fetal blood pressure.
• Placental function is essential for fetal survival and growth.

The chorion frondosum is the part of the chorion characterized by proliferation of vascularized villi adjacent to the decidua basalis, which contributes to the formation of the fetal placenta. These villi undergo extensive branching and vascularization to establish maternal-fetal exchange. In contrast, the chorion laeve is the smooth, avascular part away from the decidua basalis. Proper development of the chorion frondosum is essential for adequate placental function, supporting fetal nutrition and gas exchange throughout pregnancy.

Rationale for correct answers

B. The chorion frondosum forms from the proliferation of chorionic villi adjacent to the decidua basalis, developing into the functional fetal placenta with a dense vascular network enabling exchange of nutrients, gases, and waste. This structure is essential for sustaining fetal growth.

Rationale for incorrect answers

A. The chorion laeve, or smooth chorion, forms from villi on the side of the chorion away from the decidua basalis; these villi regress and become avascular, so it does not contribute to placental formation.

C. The yolk sac is an early embryonic structure involved in initial hematopoiesis and nutrient transfer but is not formed from chorionic villi and is distinct from the chorion.

D. The umbilical cord develops from the connecting stalk and contains blood vessels connecting fetus to placenta but is not formed by chorionic villi proliferation adjacent to the decidua basalis.

Take home points

• The chorion frondosum is the vascularized region of chorionic villi adjacent to the decidua basalis forming the fetal placenta.
• The chorion laeve is avascular and forms the smooth chorion on the opposite side of the placenta.
• Proper placental development depends on chorionic villi proliferation and vascularization in the chorion frondosum.
• The yolk sac and umbilical cord are distinct structures not formed from chorionic villi adjacent to decidua basalis.