Periods of Prenatal Development Lecture Outline Conception Periods of Prenatal Development Period of the zygote Period of the embryo Period of the fetus

Conception Ovulation: Release of ovum (egg) from one of a woman’s two ovaries Occurs approximately every 28 days Egg moves through one of the fallopian tubes toward the uterus If sexual intercourse occurs near ovulation, conception can occur A sperm must penetrate the outer membrane of the egg Each sperm and egg cell has only 23 chromosomes When merged, the resulting cell has 46 chromosomes Conception usually occurs in the fallopian tube Fertilized egg is called a zygote

Period of the Zygote (or Germinal Period) Lasts about 2 weeks, from conception through implantation   Zygote undergoes mitosis (cell duplication) as it travels down the fallopian tube to the uterus By approximately the 4th day after conception, the zygote has become a blastocyst Fluid-filled ball of cells

Two parts of the blastocyst: Inner cell mass: Cells on the inside of the blastocyst Will become the embryo Trophoblast: Cells on the outside of the blastocyst Will develop into tissues that protect and nourish the embryo

Implantation of the blastocyst into the uterine wall begins approximately 7 to 9 days post-conception Support structures begin to develop from the trophoblast after implantation

Teratogen: Any environmental agent that can cause damage during the prenatal period

General Principles of Teratogenic Effects: Dose: Larger doses over longer time periods usually have more negative effects Heredity: The genetic makeup of the mother and embryo/fetus influence the effect of a teratogen

Timing: Effects of a teratogen vary with the age of the organism at the time of exposure Sensitive Period: Time during which basic structures are being formed Each major organ system has its own sensitive period An organ system is most vulnerable to teratogens during its sensitive period

Cumulative Risk: Effect of a teratogen may be worse if there are other risk factors present (e.g., poor nutrition, lack of medical care, other teratogens)

Users would differ from non-users Article: Brown et al. (2004) Hypotheses: Users would differ from non-users Users: Lower socioeconomic status; greater obstetric risk 2. Children prenatally exposed to cocaine would differ from children without exposure in social development, but not in physical or cognitive development

Within group of women who used cocaine: Mothers who did not keep custody of their children after birth would differ from mothers who did keep custody Heavier prenatal drug use, lower SES, greater obstetric risk in mothers who did not have custody Their newborns would also show more birth complications (e.g., prematurity)

Within group of children with PCE: At 2 years of age, children in non-parental care would differ from children in parental care: Non-parental care would be higher-quality than parental care Children in non-parental care would show better cognitive and social development than children in parental care

Findings: 1. Users differed from non-users 2. Children with prenatal cocaine exposure (PCE) did not differ from children without exposure in terms of physical, social, or cognitive development

Children with PCE who were in non-parental care: 3. Mothers who retained custody did differ from mothers who did not retain custody Children with PCE who were in non-parental care: Received higher-quality care than children with PCE who remained with their biological parents Showed better social and cognitive development than children with PCE who remained with their biological parents