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