The second trimester of pregnancy extends from the 13th week until the 27th week. Early in the trimester, the fetus grows to just over 2 pounds. At the end of the second trimester, a fetus is about 12 inches long. At the end of the 16th week, the top of the uterus will be halfway between the mother's pubic bone and belly button.

By the end of the 27th week, the top of the uterus will be about 1 inch above the belly button. Through the second trimester, the fetus begins to move more and its limbs are fully formed. By the end of this trimester, the fetus can open his or her eyes and now has eyelashes. During this time it is common for the fetus to begin sucking a thumb.