TWIN PEAK SIGN (LAMBDA SIGN)

= Dichorionic Pregnancy

 

  • Zone of placental tissue extending into and tapering to a point within twin membranes  (transition zone at the intertwin membrane - placental junction)(1-3).

 

Lambda or Twin Peak sign

 

Dichorionic Twins

“T-sign” of Monochorionic Diamniotic Twins

 
  • Although it was initially described at the level of fusion between the two adjacent placentas, recent evidence suggests that it may be identified at the edge of the placentas located on opposite sides of the uterus (1,2).
  • Echo pattern similar to placenta.
  • Triangular in cross section.
  • Wider at chorion surface of the placenta.
  • Absence of "twin peak" sign neither excludes dichorionic pregnancy nor implies monochorionicity.
  • Seen in over 50% of dichorionic twins, especially in the first trimester (10-14 weeks is optimal). It may disappear by week 20 in 7% of dichorionic pregnancies with fused placentas (therefore absence after wk 20 should be viewed with caution) (4).
  • Tends to be focal occurring in one or more sites along the junction between the membranes with the placenta.

 

 

 

 

REFERENCES
  1. Wood SL, Onge R St, Connors G et.al. Evaluation of the twin peak or lambda sign in determining chorionicity in multiple pregnancy. Obstet Gynecol 1996;88:6-9.
  2. Sepulveda W, Sebire NJ, Hughes K et.al. The lambda sign at 10-14 weeks of gestation as a predictor of chorionicity in twin pregnancies. Ultrasound Obstet Gynecol 1996;7:421-423.
  3. Finberg HJ. The "twin peak" sign: Reliable evidence of dichorionic twinning. J Ultrasound Med 1992;11:571-577.
  4. Sepulveda W, Sebire NJ, Highes K et.al. Evolution of the lambda or twin-chorionic peak sign in dichorionic pregnancies. Obstet Gynecol 1997;89:439-441.