prenatal development chapter 2. the three periods of pregnancy germinal (period of the zygote)...
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Prenatal DevelopmentPrenatal Development
Chapter 2
The Three Periods of PregnancyThe Three Periods of Pregnancy
Germinal (Period of the Zygote)– First two weeks, ends with implantation
Embryonic Period– 2-8 weeks, organogenesis
Fetal Period– 9 weeks – birth (all trimesters)
Period of the Zygote (Germinal)Period of the Zygote (Germinal)
Within about 1 week of conception, cell differentiation begins
Implants (attaches to the uterine wall) on the 10th to 14th day
Embryonic Period (2-8 weeks) - OrganogenesisEmbryonic Period (2-8 weeks) - Organogenesis Neural tube develops first, will become
brain and spinal cord – rapid neuron growth, weak brain waves
Next, heart begins to pump blood The basic structure of all the organ
systems grows Eyes, ears, nose, jaw, neck, arm and leg
buds At the end of this period, it weighs less
than one ounce, about one inch long.
Called a fetus from the 8th week until birth
Fetus means fully-formed human being because all organ systems are now in place
During the 3rd month (12-16 weeks) it will have coordinated movements, be able to roll over in the amniotic fluid
Hair, eyelashes, eyebrows will grow
Period of the Fetus – Growth and Finishing Phase Period of the Fetus – Growth and Finishing Phase
– By 12th week external genitals well formed, also fingernails, toenails, tooth buds, eyelids
– Heartbeat can be heard with a special stethoscope
– End of 3 months, 3 inches, 3 ounces
– The fetus can kick, bend its arms, form a fist, curl its toes, open its mouth, suck its thumb, smile & swallow
Period of the Fetus – Growth and Finishing Phase – 3rd MonthPeriod of the Fetus – Growth and Finishing Phase – 3rd Month
– Neurogenesis, which begins earlier, proceeds rapidly (250,000 neurons per minute)
– At 20-weeks can be stimulated/irritated by sound; will shield eyes during fetoscopy
Period of the Fetus – Growth and Finishing Phase – 2nd TrimesterPeriod of the Fetus – Growth and Finishing Phase – 2nd Trimester
– The current age of viability (at which the fetus can survive outside the mother) is about 22 weeks
– 50% survive at about 25 - 26 weeks (6 months)
–95% survive at 31+ weeks
Period of the Fetus – Growth and Finishing Phase-Age of Viability
Period of the Fetus – Growth and Finishing Phase-Age of Viability
– Depends upon gestational age at birth
– BreathingHyaline membrane disease
– Regulating blood oxygen levels– Apnea– Temperature regulation– Feeding– Parenting – 47% faster weight gain &
brain development with touchKangaroo care
Problems with PreemiesProblems with Preemies
–Begins sleep-wake pattern–Responsiveness, can feel pain
after 22 weeks–React to sounds–Prefer mother’s voice–Adds fat (5 pounds)–Receives antibodies–Assumes birth position (head
down)
Fetal Period – 3rd TrimesterFetal Period – 3rd Trimester
– Any environmental agent that causes prenatal damage (leading to birth defects)
– Types – drugs, diseases, radiation, environmental pollutants
– Factors – dose, resilience (heredity), number of teratogens, gestational age at exposure (embryonic period worst)
Teratogens (Monsters) Teratogens (Monsters)
Examples– Thalidomide – 7000 infants affected
Limbs, heart, ears, kidneys, genitals
– DES (diethylstilbestrol) – reproductive problems in adult children (cancer; abnormalities in reproductive organs)
Teratogens - DrugsTeratogens - Drugs
–Don’t take anything without consulting your obstetrician
Examples–Aspirin – may be associated with
LBW, infant death, lower IQ, poor motor development
–Caffeine – LBW, miscarriage, irritable infants
Teratogens - DrugsTeratogens - Drugs
Nicotine constricts blood vessels and lessens blood flow to the uterus, causes the placenta to grow abnormally, reduces the transfer of nutrients, raises the carbon monoxide concentration in the blood stream which may damage the central nervous system
Smoking during pregnancy is associated with LBW and increased frequency of prematurity, impaired breathing during sleep, infant death and childhood cancer.
Teratogens – Why does it do this – tobacco?Teratogens – Why does it do this – tobacco?
Fetal Alcohol Syndrome (FAS/FAE) is the leading preventable cause of mental retardation.
Other symptoms include impaired motor coordination, attention, memory & language; slow physical growth & overactivity.
Facial abnormalities include widely spaced eyes, short eyelid openings, thin upper lip, small head, small upturned nose.
Teratogens - AlcoholTeratogens - Alcohol
Lesson – Women should avoid alcohol during pregnancy.
Alcohol inteferes with brain development – causing abnormalities in structure and function.
Oxygen needed for cell growth is taken from the fetus to metabolize alcohol.
Teratogens - AlcoholTeratogens - Alcohol
Rubella
HIV/AIDS
Genital herpes
toxoplasmosis
Teratogens – Infectious diseasesTeratogens – Infectious diseases
18% of women in the U.S. wait until the second trimester, and 4% until the end to get care
Many of these are unmarried, adolescent, or poverty stricken.
Reasons include lack of insurance, ambivalent feelings, high risk behaviors, and lack of transportation.
Prenatal Health CarePrenatal Health Care
Approaches to ChildbirthApproaches to Childbirth
How much medical care/availability?
Should it be natural or prepared?– Lamaze, Bradley, hypnobirthing
How about the pain?– Epidural, walking/dual-spinal epidural
How about a midwife (or a doula)?
Low Birthweight Infants (LBW)Low Birthweight Infants (LBW)
(Low)Birthweight is the best available predictor of infant survival & healthy development.
Low Birthweight Babies weigh less than 5.5 pounds.
–1 of 14 American infants–More problems with inattention,
overactivity, language delays, low IQ scores, and motor deficits
Low Birthweight Infants (LBW)Low Birthweight Infants (LBW)
–Preterm babies – born early (35/8 or fewer weeks) may be weight appropriate
–Small-for-date babies may have more serious problems.
Why so many preemies?Why so many preemies?
50% unknown
Mother’s reproductive system– Immaturity; twins
Correlation with Father’s age (older fathers)
Premature InfantsPremature Infants
Low birthweight
Very low birthweight -, 1250 grams
Many will end up normal
A higher frequency will have minor problems that show up later