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a Chapter 20 Doppler Velocimetry and Multiple Gestation 317
Table 20.2. Fetal growth restriction prediction using umbilical artery in twin-gestation pregnancies. CW continuous-wave
Doppler, S/D systolic/diastolic ratio, SGA small-for-gestational age, GA gestational age, PI pulsatility index, EFW estimated
fetal weight, RI resistance index, US ultrasonography
Reference
No. of twin
pregnancies
Method of assessment Outcome variable Sensitivity (%)
[24] 76 CW; S/D ratio differences of 1.57
or >75th percentile difference
[25] 43 CW; S/D ratio differences between
twins of >0.4
[26] 56 Duplex pulsed Doppler;
abnormal Doppler value for GA
[27] 30 Duplex pulsed Doppler;
percent difference PI umbilical artery
[28] 69 CW after real-time US;
S/D difference >0.4
[29] 58 Real-time US followed by CW;
delta S/D or EFW >15%
Birth of SGA infant 70
Birth of SGA infant 73
Weight discordance >25% 82
Unfavorable outcome
(9 of 11 were SGA)
Birth of SGA infant
Birth-weight discordance
>15%
[30] 89 CW after real-time US Birth of SGA infant
(25th percentile)
[31] 31 Duplex pulsed Doppler PI
difference > 0.5
[32] 37 Duplex pulsed Doppler;
abnormal Doppler value for GA
[33] 94 Duplex pulsed Doppler;
abnormal S/D > 95th percentile for GA
Birth-weight difference
>20%
Birth of SGA infant
( 0.40 or 1.57 demonstrated
sensitivities of 73% and 70%, respectively.
In a study of 56 twin pregnancies using real-time
and pulsed-wave Doppler ultrasonography, an abnormal
Doppler result predicted a weight discordance of
>25% with a sensitivity of 82% [26]. Adequate fetal
growth was accurately predicted in 44 of 45 normal
sets of fetuses and discordant growth in 9 of 11 twin
sets. A 50% sensitivity has been demonstrated for unsatisfactory
outcomes using abnormal umbilical artery
Doppler sonography as an end point. One such
adverse outcome was SGA which was found in 9 of 11
fetuses [27]. A 42% positive predictive value for the
birth of an SGA infant has been reported when the
intrapair difference for the S/D ratio was > 0.4 [28].
Some investigators report no difference between ultrasound-derived
EFW and the S/D ratio (intrapair
differences of >15%) for predicting the birth of discordant-weight
twins (>15% birth weight) [29]. Both
methods showed a sensitivity of 78% for these parameters
[29]. Yamada et al. [31] demonstrated a sensitivity
of 75% for a birth-weight difference of >20%
when the umbilical artery PI difference between twins
was > 0.5, similar to the 78% sensitivity reported by
Kurmanvicius et al. for birth weight discordance [34].
In summary, of the studies reviewed, a disparity
was observed for FGR prediction among the investigators,
and one-third noted sensitivities of < 50%.
Ultrasonographic Biometry
and Fetal Doppler Studies
Ultrasonographically detected differences in discordant
growth pairs can be seen as early as 23±24
weeks, with the smaller twin exhibiting a slow rate of
growth between 33 and 37 weeks (Fig. 20.5) [44]. In
pathologic twins, differences can be suggested as
early as the beginning of the second trimester.
Ultrasound measurements, such as the biparietal
diameter (BPD), are insensitive predictors of neonatal
growth discordance [23]. In twin gestations the BPD
is determined in only 79% of all fetuses, whereas