Intrauterine membranes: Sonographic findings and clinical significance

Abstract

We have identified six cases of chorioamniotic separation, three diagnosed in the third trimester and three cases seen in early pregnancy, at or prior to 16 wk' gestation. The sonographic findings consist of a fine mobile echodense line separated from the chorion and uterine wall by a lucent space. The membrane may completely surround the fetus and may extend over the fetal surface of the placenta, in which case the chorion may be identified as a separate echo. Two patients with chorioamniotic separation in the third trimester had polyhydramnios. The infants had no manifestations of amniotic band syndrome. The membranes seen in four other conditions are described and compared with chorioamniotic separation.

The empty amnion: a sign of early pregnancy failure.

“…The amniotic cavity grows much more rapidly than the chorionic cavity until approximately 14 to 16 weeks' gestation at which time the amnion and chorion fuse and the chorionic cavity is obliterated. 10 The sonographic delineation of the amnion in early pregnancy has been reported previously. Although it is a very thin membrane (0.02 to 0.5 mm in thickness), studies report its demonstration in 84 to 88% of first trimester pregnancies.n Although the amniotic sac can be detected in pregnancies as early as a little over five weeks, when it constitutes a portion of the "double bleb" sign described by Yeh and Rabinowitz,S it is usually not visualized before 6.5 weeks, at which time an embryo > 5 mm in length also is detected.…”

Chorioamniotic Membrane Separation: A Potentially Lethal Finding

“…defined: the membranes may reseal, they may remain sep arated, or they may rupture leading to an extra-amniotic pregnancy with the formation of amniotic bands. CMS followed by amnion rupture is believed to the the mecha nism responsible for the significant prenatal morbidity and mortality seen in the amniotic band syndrome [1], However, no case of prenatally diagnosed CMS has de scribed subsequent umbilical cord compromise by a seg ment of amniotic membrane [2][3][4], In our experience, CMS followed by the formation of amniotic bands proved to be life-threatening to 4 fetuses when a segment of amnion constricted the umbilical cord. The CMS seen after fetal surgery is likely different than CMS in a normal pregnancy and we hypothesize it may be more likely to lead to amniotic band formation and poten tial umbilical cord compromise.…”

“…The natural history and clinical significance of CMS in otherwise normal pregnancies has generally been repre sented as a benign finding. The incidence of CMS diag nosed by prenatal ultrasound has been reported as ranging from 1:187 to 1:4,333 [2][3][4], Of the 25 cases of CMS reported in these studies, 21 infants were delivered alive and well and the 4 deaths were from causes unrelated to the membrane separation. None of these 25 cases showed any sign of umbilical cord compromise or amniotic band formation.…”

Complete Chorioamniotic Membrane Separation

“…Of the 47 reported cases, 29 patients (62%) had amniocentesis; 2 patients (4%) underwent amniodrainage for polyhydramnios [12,14]; 5 patients (11%) had in utero fetal surgery by hysterotomy for diaphragmatic hernia [10]; 1 patient (2%) had chorion villus sampling at 9 weeks of gestation [11], and, finally, 10 cases of CMS (21%) occurred spontaneously, of whom 1 had polyhydramnios associated with encephalocele [12].…”

“…In 19 of these 47 cases (40%), the neonates were born preterm. Two of these preterm infants died during the neonatal period: 1 neonate had multiple congenital abnormalities [19], and 1 had an encephalocoele [12]. 5 of these 19 preterm infants were born by an emergency cesarean section due to fetal distress [6,10,15], with an amniotic band around the cord in 3 of these 5 cases.…”