Prenatal and Newborn Development
by Melissa L. Camp
During the first two weeks of the first trimester the zygote forms, then by weeks 3-4 the embryo forms and its primitive brain and spinal cord appear. During weeks 5-8 as an embryo its face, arms, legs, toes and fingers form as well as its internal organs. The embryo becomes a fetus during weeks 9-12 and it increases rapidly in size. Nervous system, organs, and muscles find their place and connect. The fetus is able to kick, suck their thumb, open their mouth and practice breathing. And by week 12 the sex of the fetus is evident. The second trimester occurs during weeks 13-24 and the fetus continues to grow and its movements are felt by the mother. It is sensitive to light and can react to sound. By the third trimester (weeks 25-38) the fetus can survive if it born prematurely, but it size increases, lungs mature, there is rapid brain development, and antibodies are transmitted from mother to fetus to protect against disease.