Period of the Fetus Lasts from the ninth week post-conception until the end of pregnancy (approximately 38 weeks)

1. Period of the Fetus • Lasts from the ninth week post-conception until the end of pregnancy (approximately 38 weeks)

2. Between approximately 9-12 weeks: • Organs, muscles, and nervous system start to become organized and connected • By about 12 weeks, fetus engages in most movements that are present at birth • Exs: kicking, thumb-sucking, grasping, swallowing • Expansion and contraction of lungs (“fetal breathing”) • Sexual differentiation has begun • Sex of the fetus can be detected with ultrasound by approximately 12 weeks

3. Period of the Fetus (2nd trimester): • Between approximately 16-20 weeks, mother starts to feel movement of fetus

4. Period of the Fetus (3rd trimester): • Fetus triples its weight during the last trimester • Brain growth also continues • Cerebral cortex enlarges • Fetus reacts to a variety of sounds • Age of viability: The point at which a fetus can first survive outside the womb • Approximately 22-26 weeks (with medical intervention)

5. Period of the Fetus (3rd trimester) con’t: • Near the end of pregnancy, fetus is awake more often than earlier in pregnancy • But still spends most of its time sleeping (like newborns) • REM sleep is present • Fetal activity level is correlated with infant activity level

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. Tobacco: • Most consistently associated with low birth weight, which is a risk factor for other developmental problems

12. Tobacco: Mechanisms • Nicotine constricts blood vessels • Reduces blood flow to the uterus and causes placenta to grow abnormally • Reduces the transfer of nutrients to the fetus • Nicotine raises the concentration of carbon monoxide (and decreases oxygen) in mother’s and fetus’ bloodstreams • Likely to slow fetal growth and may damage CNS

13. Fetus exposed to carcinogens contained in tobacco

14. Fetal Alcohol Syndrome: • Facial abnormalities and small head • Slow physical growth and small size • Mental retardation and/or other cognitive impairments (in memory, attention, language) • Hyperactivity • Impaired motor coordination

15. Alcohol: Mechanisms • Interferes with brain development • A woman’s body requires a lot of oxygen to metabolize alcohol • Fetus gets less oxygen