Unit 2 - Prenatal Development

Prenatal Development

• Period of the Zygote: From conception to implantation in uterine wall
• Period of the Embryo: Weeks 3 to 8
• Period of the Fetus: Weeks 9 to birth
• Zygote Timestamps: Single-cell mature ovum released from the ovary on days 9-16 of menstrual cycle; fertilization occurs within 24 hours; 2 cells at 36 hours, 4 cells at 48 hours, 16-32 cells at 72 hours; cell division forms inner cell mass at 4-5 days; blastocyst attaches to uterine wall (8-14 days).
• Blastocyst: Ball of cells formed when fertilized egg begins dividing; inner layer is the embryonic disk, which becomes the embryo; outer layer is trophoblasts (protects and nourishes embryo).
• Implantation: Blastocyst attaching to uterine wall
• Embryo Period: Formation of three cell layers (ectoderm, mesoderm, endoderm); ectoderm forms the nervous system, skin, and hair; neural tube develops from ectoderm (central nervous system); mesoderm forms muscles, bones, and circulatory system; endoderm forms digestive system, lungs, and vital organs.
• Significant Event (Week 4): Heart starts beating.
• Significant Events (Second Month): Ears, beginnings of skeleton, limbs develop.
• Embryo Size (Second Month): 2.5 cm long, 7g
• Support Structures (Post-Implantation): Amnion (watertight membrane) surrounds and cushions embryo and yolk sac, produces blood cells until the embryo develops its own blood cell production; chorion surrounds amnion and attaches to uterine tissue for nourishment and waste elimination; placenta forms from lining of chorion and uterine tissue for respiration, nutrition, and waste elimination; umbilical cord connects embryo to placenta to deliver oxygen.
• Third Month Development: Able to kick; twist; swallows; digests; urinates; male testes secrete testosterone; size 7.5 cm long; 28 g.
• Second Trimester (Months 4-6): Refined motor skills (suck thumb); mother feels the kicks; heartbeat, eyebrows, eyelashes, and hair appear; covered in vernix and lanugo.
• Vernix: White substance coating fetus to prevent chapped skin (appears 5-6 months).
• Lanugo: Fine layer of body hair allowing vernix to stick to fetus's skin (appears 5-6 months).
• Third Trimester (Months 7-9): Organ systems mature; weight gain; age of viability (22-28 weeks), possible survival outside uterus; fetus moves to head-down position; size 48-53 cm; 3.2-3.6 kg.

Teratogens

• Environmental Agents: Substances or conditions that can harm developing fetus (viruses, drugs, chemicals, radiation).
• Critical Phase of Pregnancy: When particular structures form and grow rapidly; most teratogens have strongest impact during this phase.
• Rubella: Maternal disease that can cause blindness, deafness, and cardiac effects in the unborn child. Risk greatest during first trimester.
• Toxoplasmosis: Maternal disease caused by a parasite (present in raw meat, cat feces); causes eye and brain damage; risk highest in first trimester.
• Syphilis: Sexually transmitted disease; can harm the unborn child. Risk increases as pregnancy progresses; miscarriage possible.
• Genital Herpes: Sexually transmitted disease; brain damage and neurological disorders possible during birth or contact.

Other Prenatal Development Factors

• Thalidomide: Mild tranquilizer; causes limb malformations.
• Diethylstilbestrol (DES): Synthetic hormone; linked to cervical cancer and genital abnormalities in female children.
• Fetal Alcohol Spectrum Disorder (FASD): Congenital problems resulting from alcohol consumption; self-regulation and intellectual development problems. (worse ADHD)
• Fetal Alcohol Syndrome (FAS): Severe version of FASD; microcephaly, facial malformations, hyperactivity, seizures, and low average intelligence.
• Fetal Alcohol Effects (FAE): Mild version of FASD; motor skills and attention problems are below average intellectually
• Cigarette Smoking (Pregnancy): Slows fetal growth; lower birth weights; cleft lip and palate; miscarriage or stillbirth risk.
• Cocaine Use (Pregnancy): Premature birth; smaller babies; lower IQ
• Heroin Use (Pregnancy): Increased neonatal death rate; newborns may be addicted.
• Marijuana Use (Pregnancy): Emotional, behavioral, and academic problems in the child.
• Radiation Exposure (Pregnancy): Physical deformities, intellectual disabilities, or death.

Recommendations and Safeguards

• Recommended Weight Gain (Pregnancy): 11-14 kg
• Iodine Consumption (Pregnancy): Crucial; deficiency linked to congenital hypothyroidism and cretinism.
• Folate (Folic Acid) Consumption (Pregnancy): Necessary for neural tube development; deficiency linked to spina bifida and anencephaly.
• Stress (Pregnancy): Linked to negative effects on the unborn child; prenatal growth stunting and lower birth weight are possible
• Maternal Age: Teen mothers (under 20) and mothers over 35 years of age experience heightened risks.
• Environmental Toxins: Pregnant woman and partner should attempt to limit exposure to environmental toxins.
• Safest Time Frame to Have Children: 20-35 years.