Chapter 3: Prenatal Development
How has decision making about childbearing changed over the past half-century, and what are the consequences for child rearing and child development?
Today, adults in Western industrialized nations have greater freedom to choose whether when, how to have children. In industrialized nations, family size has declined over the past half-century. But no link has been found between later birth order and lower mental test performance. Rather, less intelligent parents-as a result of heredity, environment, or both-tend to have larger families. Although reproductive capacity declines with age, adults who delay childbearing until their education is complete, their careers are established, and they are emotionally more mature may be better able to invest in parenting.
Prenatal Development
List the three phases of prenatal development, and describe the major milestones of each.
The first prenatal phase, the period of the zygote, lasts about two weeks, from fertilization through implantation of the blastocyst in the uterine lining. During this time, structures that will support prenatal growth begin to form, including the placenta and the umbilical cord.
During the period of the embryo, from weeks 2 to 8, the foundations for all body structures are laid down. the nervous system develops fastest, starting with the formation of the neural tube, the top of which swells to form the brain. Other organs follow and grow rapidly. At the end of this phase, the embryo responds to touch and can move.
The period of the fetus, lasting until the end of pregnancy, involves a dramatic increase in body size and completion of physical structures. At the end of the second trimester, most of the brain's neurons are in place. At the beginning of the third trimester, between 22 and 26 weeks, the fetus reached the age of viability. The brain continues to develop rapidly, and new sensory and behavioral capacities emerge. Gradually the lungs mature, the fetus fills the uterus, and birth is near.
The first prenatal phase, the period of the zygote, lasts about two weeks, from fertilization through implantation of the blastocyst in the uterine lining. During this time, structures that will support prenatal growth begin to form, including the placenta and the umbilical cord.
During the period of the embryo, from weeks 2 to 8, the foundations for all body structures are laid down. the nervous system develops fastest, starting with the formation of the neural tube, the top of which swells to form the brain. Other organs follow and grow rapidly. At the end of this phase, the embryo responds to touch and can move.
The period of the fetus, lasting until the end of pregnancy, involves a dramatic increase in body size and completion of physical structures. At the end of the second trimester, most of the brain's neurons are in place. At the beginning of the third trimester, between 22 and 26 weeks, the fetus reached the age of viability. The brain continues to develop rapidly, and new sensory and behavioral capacities emerge. Gradually the lungs mature, the fetus fills the uterus, and birth is near.