Amniotic Sheets — A Sheet Is Not a Band

Abstract & Commentary

By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.

Dr. Hobbins reports no financial relationship to this field of study.

Synopsis: A new study challenges the concept that the ultrasound finding of a "sheet" is innocuous.

Source: Nelson LD, Grobman WA. Obstetric morbidity associated with amniotic sheets. Ultrasound Obstet Gynecol 2010;36:324-327.

It seems that at least twice a week we either inadvertently find, or have a pregnant patient referred with a band-like structure that runs north-to-south between the uterine walls. In a non-pregnant uterus this would be called a synechium, but the most common label assigned to this finding in pregnancy is a "sheet."

The usual take on this finding, based on anecdotal experience, is that it is generally innocuous. However, two authors from Chicago recently accumulated data from 122 women noted to have amniotic sheets, and compared their outcomes with 244 matched control patients without sheets. In both groups, pregnancies with structural or chromosome abnormalities were excluded from the analysis.

Maternal outcomes included cesarean section rates, preterm birth, premature rupture of membranes, abruption, chorioamnionitis, and preeclampsia. Neonatal outcomes evaluated were birth weights < 2500 g, prematurity, and NICU admissions.

Although there was a trend toward better outcome without sheets in many of the subcategories, none of them reached statistical significance individually. Therefore, the authors lumped them together and found "composite obstetric morbidity" to be higher in those with sheets (21.3% vs 8.2%) with a relative risk of 2.6 (95% confidence interval [CI], 1.5-4.5). The cesarean section rate was significantly higher in the sheet group (38.5% vs 24.6%; 95% CI, 1.1-2.1). Neonatally, there was an increase in low birth weight (18% vs 5.3%; relative risk [RR], 3.3; 95% CI, 1.5-4.3) and admissions to the NICU (16.45 vs 7 %; RR, 2.3; 95% CI, 1.3-4.3). There were no stillbirths in the study groups and there were no differences in Apgar scores between groups.

Commentary

The results of this study surprised me. Perhaps the largest surprise was the fact that only 35% of those with sheets had had a previous dilation and curettage. This brings up the possibility that, as the authors point out, it may not be the sheet per se that is responsible for the somewhat increased morbidity, but the patient herself who may simply represent the source of increased risk. We have followed many of these patients with serial ultrasound exams and found that the sheets, while seemingly dramatic when noted at 16-24 weeks, virtually always get pushed to the side, and in late pregnancy give way to the fetus to a point where they can no longer be seen. Interestingly, the authors did not address the incidence of malpresentations or difficult deliveries.

Perhaps the greatest danger of a sheet is it being mislabeled as a "band," which then morphs into the possibility of amniotic band syndrome — something that certainly gets the attention of couples going on-line for more information. These patients look like deer in headlights when they reach our door, and it often takes more than a few minutes to peel them off the ceiling while explaining that the sheet is not a band.

This study brings up important information, but, unfortunately, it leaves us with nothing preemptive that we can do to reverse the trend in possible increased morbidity. It is heartening that there were no neonatal deaths or poorer 5-minute Apgar scores in the sheet group.