Thirteen cases of amniogenic malformations of the extremities, an incidence of one per 10,000 live births, are reviewed. Characteristic clinical features were constriction rings and/or amputations, more commonly of digits, associated with clubfoot (31%), distal syndactyly (38.5%), and edema below a constriction ring (31%). Clinical and experimental evidence strongly suggests that the pathogenesis of these defects is related to early rupture of the amnion during gestation with subsequent encirclement of fetal extremities.
Baker CJ, Rudolph AJ. Congenital Ring Constrictions and Intrauterine Amputations. Am J Dis Child. 1971;121(5):393-400. doi:10.1001/archpedi.1971.02100160063006