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Discordant fetal growth patterns in monochorionic twin pregnancies described by simple algebraic relations
Asli Umur1, Martin J C van Gemert, Arty H P Schaap
1Laser Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Objective:
To test whether twin-twin transfusion syndrome (TTTS) and non-TTTS cases that were suspect but not confirmatory for developing the syndrome (non-TTTS-with-symptoms) have discordant fetal growth patterns that correlate with our previously derived algebraic relations.
Methods:
In 25 monochorionic twin pregnancies, fetal growth was determined by standard ultrasonography. The difference between estimated fetal weights (dEFW) as well as the difference divided by the average of the two weights, the difference average ratio (DAR), were fitted to the predicted trends of discordant fetal growth for TTTS and non-TTTS pregnancies. The best fits were compared with the clinical data.
Results:
Out of 13 TTTS cases, dEFW analysis correctly correlated with 8 (62%) and DAR analysis correctly with 10 (77%). Out of 12 non-TTTS-with-symptoms cases, dEFW analysis correctly correlated with 7 (58%) and DAR analysis correctly with 9 (75%). If TTTS correlated best, dEFW analysis was correct in 8/12 (67%), and DAR analysis in 10/11 (91%) cases. If non-TTTS correlated best, dEFW analysis was correct in 7/9 (78%), and DAR analysis in 9/12 (75%). The likelihood ratios of TTTS and non-TTTS were 1.9 and 0.26, respectively, with dEFW analysis, and 9.2 and 0.31 with DAR analysis.
Conclusion:
The simple algebraic relations derived to identify trends of fetal discordant growth show evidence that clinical TTTS and non-TTTS manifestations are quantifiable. The relations may contribute to future risk stratification in monochorionic twin pregnancies, e.g., by prospectively distinguishing between cases that will develop TTTS and those that will not, despite presenting with symptoms.