AN80.1-7 | Fetal membranes — Glossary

The bushy part of the chorion facing the decidua basalis where villi proliferate; becomes the fetal part of the placenta

The smooth part of the chorion where villi atrophy; forms the outer smooth chorionic membrane

The innermost fetal membrane derived from epiblast; lines the amniotic cavity and covers the umbilical cord and fetal surface of the placenta

Fluid in the amniotic cavity; primarily fetal urine after 16 weeks; peaks at 800-1000 mL at 36 weeks; enables fetal movement and lung development

The part of the decidua underlying the embryo; forms the maternal part of the placenta

The part of the decidua overlying the embryo; stretches and atrophies as the embryo grows

The part of the decidua lining the rest of the uterus not occupied by the embryo

An extraembryonic membrane derived from hypoblast; functions include early haematopoiesis, primordial germ cell origin, and early nutrition

A remnant of the vitelline (omphalomesenteric) duct; the most common congenital gut anomaly; rule of 2s: 2% prevalence, 2 feet from ileocaecal valve, 2 inches long

A diverticulum from the hindgut extending into the connecting stalk; its vessels become the umbilical arteries and vein; remnant is the urachus (median umbilical ligament)

Mucous connective tissue of the umbilical cord rich in hyaluronic acid and type I/III collagen; cushions and protects the umbilical vessels

The layers separating maternal and fetal blood: syncytiotrophoblast, cytotrophoblast, basement membranes, villous CT, and fetal capillary endothelium

A type of placentation where maternal blood directly bathes the chorionic villi; the human placenta type

A functional unit of the placenta; the mature placenta has 15-30 cotyledons separated by decidual septa on the maternal surface

Human chorionic gonadotropin; produced by syncytiotrophoblast; maintains corpus luteum; basis of pregnancy tests; detectable from Day 8-10

Human placental lactogen; causes insulin resistance and lipolysis in the mother to provide glucose and fatty acids to the fetus

Excess amniotic fluid (>2 L); causes include anencephaly, oesophageal/duodenal atresia, maternal diabetes, and fetal hydrops

Reduced amniotic fluid (<300 mL at term); causes include renal agenesis (Potter sequence), posterior urethral valves, IUGR

Abnormal placentation where chorionic villi reach the myometrium without intervening decidua (Nitabuch's layer absent); causes massive PPH

A zone of fibrinoid degeneration in the decidua basalis; the natural cleavage plane for placental separation after delivery; absent in placenta accreta

Cord containing only one artery and one vein instead of the normal two arteries and one vein; associated with congenital anomalies in 30% of cases

The space between chorionic villi filled with maternal blood; the site of maternal-fetal exchange in haemochorial placentation

A constellation of pulmonary hypoplasia, limb deformities, and characteristic flat facies caused by severe oligohydramnios from renal agenesis