Relative atony of myometrium underlying the placental site secondary to high cornual implantation—A major cause of retained placentas

Abstract

1.1. During fifteen hundred deliveries it was necessary to remove the placenta manually 62 times. Of these retained placentas, 72.6 per cent were found to be implanted in the cornual portion of the uterus. Musculature under these placental sites was unusually thin and relatively atonic.2.2. During one hundred consecutive deliveries the placenta was located by intrauterine palpation immediately after the second stage and the thickness and tone of musculature underlying the placental site were estimated by bimanual palpation immediately after the third stage. Musculature underlying cornual placental sites was relatively atonic and the average thickness was estimated to be one-third that of the firm musculature underlying all other placental sites.3.3. Twenty-five placentas were manually removed immediately after delivery of the baby, and the thickness and tone of musculature underlying respective placental sites were estimated in relation to the same characteristics of the other uterine walls. The musculature of placental sites on the anterior and posterior walls was almost as thick and firm as the other walls of the same uteri. Placental site musculature in the fundus was somewhat thinner and softer. Placental site musculature in the cornua was obviously thinner and relatively atonic.4.4. The evidence indicates that the primary cause of retention of many placentas is a relative atony of the musculature underlying placentas implanted high in the cornual region. Constriction below such placentas is due to the normal third-stage retraction, and should be considered more a result of placental retention than a cause of it.5.5. Palpable asymmetrical bulging of a uterine horn during a prolonged third stage should lead the obstetrician to suspect this phenomenon as the cause of retention. Occasionally a cornually implanted placenta may be suspected during labor when one cornu is bulbous and contracts poorly.