Welcome to the second trimester! This week's big developments: Your baby can now squint, frown, grimace, pee, and possibly suck his thumb. Thanks to brain impulses, his facial muscles are getting a workout as his tiny features form one expression after another. His kidneys are producing urine, which he releases into the amniotic fluid around him — a process he'll keep up until birth. He can grasp, too, and if you're having an ultrasound now, you may even catch him sucking his thumb. In other news: Your baby's stretching out. From head to bottom, he measures 3 1/2 inches — about the size of a lemon — and he weighs 1 1/2 ounces.