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 categorised 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 anaemia 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
- 1. Schmidt W, Kurjak A. Color Doppler Sonography in Gynecology and Obstetrics. Thieme Medical Publishers. (2004) ISBN:1588902560. Read it at Google Books - Find it at Amazon
- 2. Caravello JW, Chauhan SP, Morrison JC et-al. Sonographic examination does not predict twin growth discordance accurately. Obstet Gynecol. 1997;89 (4): 529-33. doi:10.1016/S0029-7844(97)00010-0 - Pubmed citation
- 3. Nyberg DA, McGahan JP, Pretorius DH. Diagnostic imaging of fetal anomalies. Lippincott Williams & Wilkins. (2003) ISBN:0781732115. Read it at Google Books - Find it at Amazon
- 4. Sonntag J, Waltz S, Schollmeyer T et-al. Morbidity and mortality of discordant twins up to 34 weeks of gestational age. Eur. J. Pediatr. 1996;155 (3): 224-9. - Pubmed citation
- 5. Banks CL, Nelson SM, Owen P. First and third trimester ultrasound in the prediction of birthweight discordance in dichorionic twins. Eur. J. Obstet. Gynecol. Reprod. Biol. 2008;138 (1): 34-8. doi:10.1016/j.ejogrb.2007.08.004 - Pubmed citation
- 6. Victoria A, Mora G, Arias F. Perinatal outcome, placental pathology, and severity of discordance in monochorionic and dichorionic twins. Obstet Gynecol. 2001;97 (2): 310-5. - Pubmed citation
- 7. Machin GA. Velamentous cord insertion in monochorionic twin gestation. An added risk factor. J Reprod Med. 1997;42 (12): 785-9. - Pubmed citation
- 8. D'Antonio F, Khalil A, Mantovani E et-al. Embryonic growth discordance and early fetal loss: the STORK multiple pregnancy cohort and systematic review. Hum. Reprod. 2013;28 (10): 2621-7. doi:10.1093/humrep/det277 - Pubmed citation
- 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
- 10. Bora SA, Bourne T, Bottomley C et-al. Twin growth discrepancy in early pregnancy. Ultrasound Obstet Gynecol. 2009;34 (1): 38-42. doi:10.1002/uog.6422 - Pubmed citation
- 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