Classification of discordant fetal growth may contribute to risk stratification in monochorionic twin pregnancies

To determine whether classification of discordant growth between fetal twins allows risk stratification in monochorionic twin pregnancies. In 12 twin-to-twin transfusion syndrome (TTTS) pregnancies and 12 cases that were suspected of developing the syndrome, fetal growth was determined by serial standard sonography. Fetal growth was expressed as the difference-average-ratio (DAR), defined as the difference in estimated fetal weight between both twins divided by their average weight. In each case, we determined the maximum value of DAR and the rate of change of DAR using a least squares linear fit of the estimated fetal weights. For the TTTS cases the maximum value of DAR was 0.44 +/- 0.21 versus 0.52 +/- 0.13 for the suspected TTTS cases (P = 0.25). The rate of change of DAR was 0.052 +/- 0.034 per week for the TTTS versus 0.0055 +/- 0.0092 for the suspected TTTS cases (P = 0.0004). After laser therapy, DAR decreased in four successful cases, with a rate of change of -0.0146 +/- 0.0093 per week, but increased further in one unsuccessful case, due to patent anastomoses. In the seven TTTS cases treated with amnioreduction, DAR did not decrease; in one of two suspected TTTS cases the DAR decreased slightly. In the nine amnioreduction cases, the average rate of change of DAR was 0.067 +/- 0.083 per week. This was significantly different from the four successful laser cases (P = 0.01). The rate of change of DAR, but not DAR itself, has prognostic value for the development of suspected TTTS pregnancies, for the onset and severity of TTTS and for the efficacy of therapy. This parameter is derived from routine sonography examination and may contribute to risk stratification in monochorionic twin pregnancies