PS275 - chapter four

Prenatal Period

• The time before birth

• Total period of time from conception to birth is 266 days or 38 weeks

• Gestation period - conception to birth + 2 weeks

• Time of most rapid growth and development in a person’s life

• Used to count age from when we were conceived!

Normal Prenatal Period

• Process of maturation

• Changes & growth that occur in an orderly, predictable sequence

• Due to genetic z7 biological programming

• Environmental factors

3 Periods in Prenatal Development

1. Period of the zygote (germinal period)

• Conception to 2 weeks

2. Period of the embryo

• Weeks 3-8 of development

3. Period of the foetus

• Week 9 to birth

The Period of the Zygote

• As the zygote moves down the fallopian tube toward the uterus, it divides by mitosis into two cells

• Continue to divide forming a blastocyst

Blastocyst: ball of cells formed when the fertilised egg first begins to divide

• Inner layer of blastocyst (embryonic disk) becomes the embryo

• Starts implantation (burrowing of the blastocyst into the lining of the uterus)

  • Blastocyst communicates with uterine wall, position, attach, invade

  • Takes 48 hours, 7-10 days after ovulation

  • ¾ zygotes fail to survive the initial phase of prenatal development (miscarriage)

• Once implanted, blastocyst starts making support structures

Amnion: watertight membrane that surrounds the developing embryo, serving to regulate temperature and cushion against injuries

• The chorion is another membrane which becomes the lining of the placenta

The Period of the Embryo

• Lasts from implantation through the eighth week of pregnancy

• By third week, the blastocyst (embryonic disk) differentiates into three layers

  • Development begins of neural tube (beginning of nervous system & brain)

  • Outer cell layer in blastocyst forms amniotic sac, placenta, chorion, and umbilical cord

• During second month embryo looks way more human

• During 7th-8th prenatal weeks, embryos sexual development starts with genital ridge called the indifferent gonad

The Period of the Foetus

• Last seven months of pregnancy; major organ systems, foetus moves, senses, and behaves

• 12 weeks after conception, foetus is 7.5cm long, and weighs almost 28g

• 3rd month foetus can swallow, digest, and urinate, also start sexual differentiation

• 4-6 months (second trimester) can make movements

Vernix: white, cheesy substance that covers the foetus to protect skin from chapping

Lanugo: find hair covering the foetus’s body that helps vernix stick to the skin

• 7-9 months is the finishing phase, preparing foetus for birth

  • In 9th month assumes head-down position - foetus drops

Age of viability: point between the 22nd-28th prenatal weeks when survival outside the uterus is possible

Can Unborn Babies Distinguish & Recognize Sound?

INFLUENCES ON PRENATAL DEVELOPMENT: ENVIRONMENT

Prenatal development: process of maturation that typically happens under ideal conditions

Development is Altered By…

• Genetically healthy embryo may be damaged by environmental factors

• Genetic abnormalities may be exacerbated by environmental conditions

Teratology

Teratology: study of developmental abnormalities

Teratogen: any environmental factor that disturbs the development of a foetus

• Includes drugs, tobacco, alcohol, hormones, radiation, chemicals, maternal diseases

• All lead to congenital or long-term physical/health/behavioural impacts

• Our goal is prevention!

How Teratogens Influence Development

1. Affect the mother during pregnancy

• Mother’s exposure (or lack of exposure) to the factor often impacts physical development

• Ex. babies born blind in London!

2. Affect the mother before conception

• Ex. accutane

3. Affect the father before conceptions

• Alter sperm cells (impacting zygote’s genetics)

  • meds/alcohol/cocaine

  • Workplace chemicals

4. Transfer from partner to mother during pregnancy

• Touching work-related chemicals on clothes

• Chemicals in 2nd-hand smoke

5. Produce behavioural, learning, and psychological problems

• Heroin/alcohol exposure

6. Produce effects that do not appear until child is much older

• Hormone DES

Sensitive period: limited time span during which a body part / system develops most rapidly

The Greatest Period of Risk

• 1st 8-10 weeks are the most at risk!

Thalidomide Drug Effect

• The drug thalidomide

• Used to promote safe, sound sleep from 1959-1962

• Also relieved symptoms of morning sickness

• Estimate of 10k-20k babies born with abnormalities!

  • Missing ears, blindness, disfigurement, cleft palate, internal organ problems, phocomelia

Phocomelia: variety of malformations of limbs

• The type of malformation determined by the timing of drug use

• Specific times during 1st trimester lead to specific abnormalities

Smoking During Pregnancy

• 10.7% of female adults in Canada smoke

• In high-income countries, 1 in 10 women smoke tobacco

• Typically produces low birth weight (LBW)

  • Usually under 5.5lbs

  • Means delivering early sometimes! NOT GOOD

Alcohol Consumption During Pregnancy

• Relationship between drinking during pregnancy and miscarriage, physical malformations, and learning disabilities / behaviour problems

FAS: group of abnormalities associated with prenatal alcohol exposure

• Three diagnoses for alcohol consumption during pregnancy

Streissguth & Colleagues

• 500 women & their kids beginning in early pregnancy

• Good diets, well-educated, middle-class, no drugs, DID DRINK 

• Longitudinal study intended to study long-term effects

• Light to moderate amounts STILL related to a variety of problems in childhood