Many have marveled at this picture of Byron and Lincoln, identical twin brothers with dramatically differing birthweights. While their situation was likely the result of Twin-to-Twin Transfusion Syndrome (TTTS), size discrepancy in twin pregnancy can be a worrisome issues for parents. Thorn663 posted the following in the message forum... "I found out at 5 weeks that I'm pregnant with fraternal twins (first pregnancy). On the ultrasound, one gestational sac was significantly smaller than the other one. The MD said that the bigger twin looks great but he was unsure about the viability of the smaller one. I went back for another ultrasound today (6 weeks and 4 days pregnant). We saw two heartbeats, which was reassuring, however, the one twin is still about half the size of the other. Has anyone else had the same experience? If so, what was the outcome? I'm a bit nervous for the little one." Read the reassuring responses from other parents.