Your baby is an embryo consisting of two layers of cells from which all her organs and body parts will develop. 4 weeks pregnant. 5 weeks pregnant. 6 weeks pregnant. 7 weeks pregnant. Twins – 3 weeks pregnant. Twins – 4 weeks pregnant.
A baby in the first trimester at 12 weeks has the following features: Muscles and nerves are coordinated. Baby can make a fist. The baby’s eyelids are closed and will not open until 28 weeks’ gestation. The growth of the head is slower and the baby has grown longer. Your baby weighs nearly one ounce and is about 3 inches long.
Pregnancy and Fetal Development. Picture of First Trimester (4 Weeks) First Trimester: The Baby at 4 Weeks. Your baby’s brain and spinal cord have begun to form. The heart begins to form. Arm and leg buds appear.