Trends of discordant fetal growth in monochorionic twin pregnancies

We derived simple analytical relations representing trends of discordant fe tal growth in monochorionic twins developing the twin-twin transfusion synd rome from an approximation of previously developed model equations. In seve re twin-twin transfusion syndrome cases, the difference between the estimat ed fetal weights of both twins increases proportional to (t- 5)(5) (t denot es gestational age in weeks) and the sum of both weights increases proporti onal to t(3). Hence, the ratio between the difference of estimated fetal we ights and the average of the two weights (difference average ratio) increas es in proportion to (t - 5)(5)/t(3). I, mild cases, the difference between estimated fetal weights as well as the sum of the two weights increases pro portional to t3. Therefore, the difference average ratio becomes a constant . Comparison with clinical data of severe and mild cases showed surprisingl y good agreement except after laser coagulation of placental anastomoses. T hese relations may therefore enable us to distinguish between severe and mi ld developing twin-twin transfusion syndrome cases.