Quick update: Our little guy/girl is definitely moving around a lot! The doctor said I probably won't be able to tell the difference between baby movements and other intestinal movements for another couple weeks, but it is already so obvious to me. This baby is definitely an active one! Here's what www.babycenter.com had to say about week 18:
Head to rump, your baby is about 5 1/2 inches long (about the length of a bell pepper) and he weighs almost 7 ounces. He's busy flexing his arms and legs — movements that you'll start noticing more and more in the weeks ahead. His blood vessels are visible through his thin skin, and his 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 his nerves, a process that will continue for a year after he's born. If you're having a girl, her uterus and fallopian tubes are formed and in place. If you're having a boy, his genitals are noticeable now, but he may hide them from you during an ultrasound.