The association between uterine synechiae and prior uterine procedures (i.e., dilatation and curettage) has been well documented. When pregnancy occurs, the amnion and chorion envelope the synechia. Hence, the fetus is exposed to only intact amnion and is, therefore, protected from the potential disruptive effects associated with the amniotic band syndrome.
The position of a synechia may prevent the fetus from attaining a longitudinal lie. Hill and Mills have reported a case of umbilical cord prolapse through a transverse uterine synechia with subsequent fetal demise. In contrast to an amniotic sheet, the placenta may abut against or extend along a uterine synechia.
The differential diagnosis of a uterine synechia include the amniotic band syndrome and an amniotic sheet. An amniotic band is a filmy membrane that may be identified attached to a specific congenital disruption (i.e., encephalocele). A uterine synechia is thicker and straighter than an amniotic band. Since a uterine synechia is surrounded by amnion, it is not associated with fetal anomalies due to disruption of normal embryologic development.
A uterine synechia is usually thicker than an amniotic sheet.
On a longitudinal view, the central synechia is relatively hypoechoic, while the surrounding membranes are more echogenic.