From the "Pregnancy Calendar"

Size
Your baby is about 1 3/4 to 2 1/2 inches long and weighs about a third of an ounce, the size of a peanut.

Development
This is a big week for your baby's growth -- she'll double in height. At the end of the week, her head and body will be roughly equal in length. This week also starts an active phase for her-she can turn somersaults, roll over, flex her fingers, hiccup, and stretch. You won't be able to feel her movement for another month and a half. She's floating in lots of amniotic fluid. Her limbs are developing from webbed paddles into arms and legs that have well-defined fingers and toes. Fingernails, toenails, and hair follicles are also beginning to form.

Reprinted with permission from Great Expectations: Your All-in-One Resource for Pregnancy & Childbirth. Copyright 2004 by Sandy Jones, MA and Marcie Jones, MA. Used with permission from Barnes & Noble Books, an imprint of Barnes & Noble Publishing, Inc.
http://parenting.ivillage.com/pregnancy/calendar/frame/0,,,00.html?downDate=2005-10-25