Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood.
They are an essential element in pregnancy from a histomorphologic perspective, and are, by definition, a product of conception. Branches of the umbilical arteries carry embryonic blood to the villi. After circulating through the capillaries of the villi, blood returns to the embryo through the umbilical vein. Thus, villi are part of the border between maternal and fetal blood during pregnancy.
Anchoring (stem) villi stabilize the mechanical integrity of the placental-maternal interface.
Development
The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. They undergo several stages, depending on their composition.
Stage
Description
Period of gestation
Contents
Primary
The chorionic villi are at first small and non-vascular.
Until about the end of the second month of pregnancy, the villi cover the entire chorion, and are almost uniform in size—but after then, they develop unequally.
The bulk of the villi consist of connective tissues that contain blood vessels. Most of the cells in the connective tissue core of the villi are fibroblasts. Macrophages known as Hofbauer cells are also present.
Recent studies indicate that the chorionic villi may be susceptible to bacterial[5] and viral infections. Recents findings indicate that ureaplasma parvum can infect the chorionic villi tissues of pregnant women, thereby impacting pregnancy outcome.[6] DNA from JC polyomavirus and Merkel cell polyomavirus has been detected in chorionic villi from pregnant women and women affected by miscarriage.[7][8] DNA from BK polyomavirus has also been detected in the same tissues but to a lesser extent.[7]
In early miscarriage, the finding of chorionic villi in vaginal expulsions is often the only definite confirmation that there was an intrauterine pregnancy rather than an ectopic pregnancy.
