About two weeks before your expected period. A sperm joins with the ovum (egg) to form one cell. When conception (fertilization) occurs, the baby's features, including sex, hair and eye color, are determined. The new life has begun. A few days after your missed period. The baby's heart begins to beat. 4 weeks after conception. The backbone and muscles are forming. Arms, legs, and ears have begun to show. 5 weeks after conception. Five fingers can be discerned in the hand. 8 weeks after conception. The baby hiccups and reacts to loud noises. Everything is now present that will be found in a fully formed adult. 12 weeks after conception. The baby can grasp an object placed in his or her hand and make a fist. 14 weeks after conception. At 16 weeks, doctor's can use ultrasound to determine the baby's gender. 20 weeks after conception. The baby's eyelashes can be seen and the lungs are developing.