description
- twin growth discordance is the inter-twin discrepancy in the sonographic estimated fetal weight greater than 20%.
- in general it is caused by placental insufficiency resulting in growth restriction of one twin. genetic and structural anomalies must also be excluded in the smaller twin.
diagnosis
the standard care for twin pregnancy includes serial sonographic evaluation to assess growth of each fetus.
findings suggestive of growth discrepancy include:
- estimated fetal weights discordant by more than 20%
- abdominal circumference divergent by 20 mm or more.
- biparietal diameter differences greater than 6 mm, with the smaller biparietal diameter less than 2 standard deviations below the mean.
- head circumference divergent by more than 5%
- umbilical artery s/d ratio discordancy greater than 15%, or elevated in one or both twins.
differential diagnosis
twin-twin transfusion is the main differential diagnosis.
the visualization of discordant sexes or dichorionic placentation excludes this possibility.
chromosomal abnormality of the smaller twin may be considered, especially in the presence of structural markers.
sonographic features
- estimated fetal weights differ by >20%
- ac by >20mm
- bpd by >6 mm, with the smaller < 2 sd below the mean
- hc by >5%
may be abnormalities in umbilical or fetal dopplers consistent with growth restriction.
associated syndromes
references
- forouzan i, graham e, morgan ma reduction of right atrial peak systolic velocity in growth-restricted discordant twins.
am j obstet gynecol oct;175(4 pt 1):1033-1035 1996 - rizzo g, arduini d, romanini c cardiac and extracardiac flows in discordant twins.
am j obstet gynecol may;170(5 pt 1):1321-1327 1994 - yalcin hr, et al. the significance of birth weight difference in discordant twins: a level to standardize?
acta obstet gynecol scand. jan; 77(1): 28-31. 1998