Twin growth discordance

Twin growth discordance is a term used in obstetric imaging to describe a significant size or weight difference between the two fetuses of a twin pregnancy. To be classified as a growth discordance, some consider that the estimated fetal weight (EFW) of the smaller twin should fall under the 10th centile.

A twin growth discordance may occur in up to 25% of twin pregnancies. It is more common in monochorionic pregnancies.

Depending on the parameter involvement this may be categorized as:

  • weight discordance (interpair weight disparity of greater than 25% 2): this usually occurs when there are factors that affect the twins asymmetrically, possible risks that are associated with IUGR.
  • size discordance: this is usually associated with anemia and it can happen as a result of twin-twin transfusion.

In the early first trimester, the difference in crown-rump length (CRL) may be used as a parameter. 

During later stages size discordance is better assessed using the abdominal circumference (AC) 2,3 and the disparity of 20mm or more are usually taken as a cut-off value for considering the pregnancy as discordant. The accuracy of using the abdominal circumference is however disputed by some authors 2.

A weight discordance is assessed by taking considering the estimated fetal weight (EFW) difference at 20-25% 2-4.

Twin pairs with growth discordance in which one twin is small for gestational age, have an increased risk of neonatal death

Share article

Article information

rID: 13605
System: Obstetrics
Synonyms or Alternate Spellings:
  • Discordant fetal growth
  • Discordant twin growth
  • Growth disordant twins
  • Fetal growth discordance
  • Fetal biometric discordance
  • Twin growth discrepanacy
  • Growth discrepancy in twins
  • Growth discrepancy in twin pregnancies

Support Radiopaedia and see fewer ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.