Double Bleb Sign
Clinical Significance
The double bleb sign is a normal ultrasonographic finding of early intrauterine pregnancy (approximately 5-6 weeks gestational age), representing the amniotic sac and yolk sac appearing as two small bubbles attached to the gestational sac wall, with the embryonic disc located between them. 1
This sign has no relationship to abdominal trauma, surgery, or infection and should not be confused with other radiologic findings in acute abdominal conditions.
Key Distinguishing Features
Normal Obstetric Finding
- The double bleb sign appears at approximately 25-40 days menstrual age as the earliest evidence of an embryo, occurring about 2 weeks after the initial appearance of the gestational sac 1
- The two "blebs" represent:
- The amniotic sac
- The yolk sac
- The embryonic disc is positioned between these structures 1
Not to Be Confused With
- Double target sign: This is a completely different finding seen in pediatric intussusception, representing two concentric "target" lesions indicating double intussusception 2
- This appears on abdominal ultrasound in children with acute abdominal pain and requires urgent reduction 2
Clinical Context and Management
If Identified in Pregnancy Context
- The double bleb sign, along with the intradecidual sign, represents one of the most important confirmatory signs of early intrauterine pregnancy 1
- No intervention is required - this is a normal developmental finding 1
- Confirms viable intrauterine gestation and helps exclude ectopic pregnancy 1
If Question Relates to Abdominal Trauma/Surgery
The provided evidence regarding abdominal trauma management 3, 4, 5, 6, 7 does not reference any "double bleb sign" as a relevant finding. In trauma patients:
- Bedside ultrasound (FAST) should be the initial diagnostic modality in hemodynamically unstable patients with blunt abdominal trauma to identify free intraperitoneal fluid 3
- FAST has 83% sensitivity and 100% specificity for identifying intra-abdominal injuries requiring intervention 3
- All intra-abdominal injuries from blunt trauma manifest clinical signs or symptoms within 8 hours 25 minutes of hospital arrival 7
Critical Pitfall to Avoid
Do not misinterpret the obstetric "double bleb sign" as a pathologic finding requiring intervention - it is a normal developmental milestone in early pregnancy 1. If the clinical context involves abdominal pain in a patient with prior surgery or trauma, focus on appropriate trauma imaging (CT with contrast, FAST) rather than obstetric ultrasound findings 3, 4.