Hysterographic double-outlined uterine cavity: a sign of unsuspected pregnancy.

A review of three hysterograms inadvertently performed during early pregnancy reaffirms the regular appearance of infiltration of aqueous opaque media into the substance of the decidua, producing the sign of the double-outlined uterine cavity. Although such endometrial opacification may also occur during the late secretory phase, its recognition should arouse suspicion of pregnancy. A coexisting intrauterine filling defect may then be more confidently diagnosed as an amniotic sac.