One of the exciting parts of pregnancy is understanding how your baby is developing and growing. A spinal cord develops about two weeks after sperm fertilizes an egg. The baby's head and body develop after six weeks of pregnancy. The heart, eyes, brain, mouth, inner ears, and digestive system begin to form. There are tiny buds that will become arms and legs. During the second month, development is very rapid as all of your baby's major body organs and body systems, including the lungs, liver and stomach start to develop. The ears and eyelids form. Ankles, toes, wrists, fingers, and sexual organs develop. At the end of the second month your baby looks like a miniature human infant - a little over an inch long, or three centimeters long, and weighing less than one ounce or 28 grams.