double bleb sign

 double bleb sign is a sonographic feature where there is visualization of a gestational sac containing a yolk sac and amniotic sac giving an appearance of two small bubbles 2.

The embryonic disc is located between the two bubbles

The “double-bleb sign” is a transient appearance that can be seen in the gestational sac.

It is produced by the yolk sac and probably the amniotic cavity.The trilaminar embryo is not yet visible at this stage.

The embryo can be detected when it is approximately 2 mm in length as an area of asymmetrical thickening of the yolk sac.

It is not unusual to only demonstrate cardiac motion when the crown rump length (CRL) of the embryo reaches 5-6 mm.

The amniotic sac is small and closely applied to the fetus and cannot be appreciated as a separate structure until there is sufficient amniotic fluid to separate the amnion from the embryo.