Placental Changes in Amniotic Band Sequence, Extra-Amniotic and Extramembranous Pregnancy

Abstract

Three entities, characterized by rupture of the amnion, are described. Amniotic band sequence is a group of congenital abnormalities with a variable spectrum of abnormalities characterized by formation of fibrous bands or sheets from the placenta attaching to fetal structures. The placenta often shows an intact, somewhat thickened chorion and a globular portion of disrupted amnion at the base of the umbilical cord with small tethers to the cord. Extra-amniotic and extramembranous pregnancy are rare events in which the fetus develops partially or completely outside intact membranes. Extra-amniotic pregnancy occurs with complete amnion rupture sufficiently early, or late, in gestation with no fetal sequelae of amniotic band formation. It results in a small, thick remnant of amnion remaining attached to the proximal umbilical cord within an intact chorionic membrane. Disruption of both amnion and chorion in early to mid-gestation results in extramembranous pregnancy associated with placental circumvallation and high fetal morbidity. Residual membranes are short and thick comprising a restrictive sac insufficient to contain the developing fetus.