Because we are twins, and because we share a placenta, we get ultrasounded frequently. Compare Baby A from January 11 and January 25 and see how much bigger we are!
January 11:

January 25 (the picture is a little blurrier, but compare head size with the previous picture. That's Baby B's arm floating above Baby A's abdomen):

Today our estimated fetal weight was almost 700 grams-- we each weigh about 1 pound 8 ounces! We continue to share our placenta nicely and both have good fluid levels.
We are very active and certain fetuses-- not to name names, but this would be Baby A-- kept kicking the ultrasound probe during our scan today. The poor ultrasound tech had to try 4 times to get a nice view of the heartrate because of all the kicking.
Our next ultrasound is in 2 weeks, and we plan to continue growing in the meantime.