By the fifth week of your pregnancy, your future son or daughter is officially an embryo, according to the MayoClinic.com. Embryos are comprised of three layers of cells, skin, organs and tissues; the scientific names for these layers are ectoderm, mesoderm and endoderm. As your pregnancy progresses, the embryo will shape into a fully formed baby ready for a safe and healthy delivery.

The First Weeks

In the first four weeks of pregnancy, your future child isn’t officially an embryo but medically called a zygote. By the time your future child becomes an embryo, you’re about halfway through the first trimester. During this stage of your pregnancy, the embryo’s brain, heart and spinal cord have begun to form in its middle layer of skin or the mesoderm; the embryo itself is about 1 to 3 mm long or the size of a pencil tip. Your future son or daughter will also adopt the curvature of a baby’s body rather than that of a round zygote.

The Next Weeks

As the weeks pass, your future child’s basic facial features will begin to form and small buds that ultimately grow into arms and legs also form. By week 10, your embryo’s genitals are beginning to develop, but you and your doctor will not be able to determine the gender of your future child yet. Your future child is able to move around within the womb, but you won’t be able to feel those nudges and kicks just yet. Your baby’s upper lip also forms during this embryonic stage of your pregnancy.

The Final Stages

Each stage of pregnancy is called a trimester, but by the end of the first trimester, your future child is no longer medically considered an embryo but a fetus. The average early-stage fetus is about 2 inches in length and weighs about 1/2 oz. Red blood cells, organs, genitals and limbs fully develop during the fetal stage of pregnancy. Once you hit week 11 of your pregnancy, you still have about 29 weeks to go until you give birth. Some women may go into labor even earlier; if premature labor happens during the 28th week of pregnancy or later your child has at least a 90 percent chance of surviving without suffering significant medical challenges later in life.