Well I am sure you have read all the other posts, so I will just add my comments to what Baby Center had to say about our 18 week baby! My comments are in pink.
Head to rump, your baby is about 5 1/2 inches long (about the length of a bell pepper) (she measured right on target for this) and she weighs almost 7 ounces (ours is closer to 10). She is busy flexing his arms and legs (ummm not this morning, but I have felt her a lot this afternoon) — movements that you'll start noticing more and more in the weeks ahead. Her blood vessels are visible through his thin skin, and her ears are now in their final position, although they're still standing out from his head a bit. A protective covering of myelin is beginning to form around her nerves, a process that will continue for a year after she's born. If you're having a girl, her uterus and fallopian tubes are formed and in place (yeah baby).