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

2. 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

3. 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

4. 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

5. 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

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

7. 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

8. 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

10. 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)

11. 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

12. 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)

13. 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

14. 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

15. 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