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.
intrauterine growth restriction (IUGR) in the smaller twin:
- depending on the definition the smaller twin must have IUGR according to some authors.
- otherwise: the greater the discordance the higher the likelihood
- placental insufficiency
- twin-twin transfusion syndrome
- higher incidence with a velamentous cord insertion 6
- higher incidence with single umbilical artery 6
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.
Ancillary sonographic features include
- oligohydramnios in smaller twin (especially if discordance is severe)
Twin pairs with growth discordance in which one twin is small for gestational age, have an increased risk of neonatal death
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- 9. Salomon LJ, Cavicchioni O, Bernard JP et-al. Growth discrepancy in twins in the first trimester of pregnancy. Ultrasound Obstet Gynecol. 2005;26 (5): 512-6. doi:10.1002/uog.1966 - Pubmed citation
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- 11. Puccio G, Giuffré M, Piccione M et-al. Intrauterine growth pattern and birthweight discordance in twin pregnancies: a retrospective study. Ital J Pediatr. 2014;40 (1): 43. doi:10.1186/1824-7288-40-43 - Free text at pubmed - Pubmed citation