Prenatal Development

Chapter 2

Biological Beginnings: Conception

 Ova are released from the ovaries and travel down the fallopian tubes, where conception occurs. Development begins at conception.  Males produce an average of 300 million sperm per day. Only 300-500 reach the ovum.

 Sperm can live for 6 days and ova for one.

The 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)

 4 th day – blastocyst, hollow, fluid filled ball (60-70 cells) – Inside, embryonic disk will become new organism – Outside, troboblast, protective covering

Period of the Zygote (Germinal)

 Within about 1 week of conception, cell differentiation begins  Implants (attaches to the uterine wall) on the 10 th to 14 th day

Period of the Zygote (Germinal)

 Troboblast will form the amnion (fluid sac which regulates temperature and forms a cushion)  Will also form the chorion, from which fingerlike villi or blood vessels emerge and the placenta forms as they burrow into the uterine lining .

Embryonic Period – 3

rd

after conception week

 Umbilical cord connects the growing organism to the placenta  It has one vein and two arteries  The mother’s and embryo’s blood will not mix directly (red blood cells, bacteria, hormones, maternal waste are filtered)

Embryonic Period – 3

rd

after conception week

 Embryonic disk forms: – Ectoderm – skin and nervous system – Mesoderm – muscles, skeleton, circulatory system – Endoderm – digestive system, lungs, urinary tract, glands

Embryonic Period (2-8 weeks) - Organogenesis

 Neural tube develops first, will become brain and spinal cord  Next, heart begins to pump blood  The basic structure of all the organ systems grows  Eyes, ears, nose, jaw, neck, arms legs, fingers & toes form  At the end of this period, it weighs less than one ounce, about one inch long.

Period of the Fetus – Growth and Finishing Phase – 3 rd Month –

The fetus can kick, bend its arms, form a fist, curl its toes, open its mouth, suck its thumb, smile & swallow

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By 12 th week external genitals well formed, also fingernails, toenails, tooth buds, eyelids

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Heartbeat can be heard with a special stethoscope

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End of 3 months, 3 inches, 3 ounces

Period of the Fetus – Growth and Finishing Phase 

Called a fetus from the 8 th week until birth

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Fetus means fully-formed human being because all organ systems are now in place

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During the 3 rd month (12-16 weeks) it will have coordinated movements, be able to roll over in the amniotic fluid

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Hair, eyelashes, eyebrows will grow

Period of the Fetus – Growth and Finishing Phase – 2 nd Trimester –

Mother can feel movements

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Can hear heartbeat with ordinary stethoscope

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Neurogenesis proceeds rapidly (250,000 neurons per minute)

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At 20-weeks can be stimulated/irritated by sound; will shield eyes during fetoscopy

Period of the Fetus – Growth and Finishing Phase-Age of Viability –

Age at which the fetus can survive outside the mother (38-40 weeks is full term)

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5% survive at 22 weeks

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50% survive at 26 weeks (6 months)

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95% survive at 28 weeks

Problems with Preemies

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Depends upon gestational age at birth

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Breathing

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Hyaline membrane disease

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Regulating blood oxygen levels Apnea Temperature regulation Feeding Parenting – 40% faster weight gain & brain development with touch

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Kangaroo care

Fetal Period – 3 rd Trimester –

Begins sleep-wake pattern

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Responsiveness, can feel pain after 24 weeks

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React to sounds

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Prefer mother’s voice

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Adds fat (5 pounds)

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Receives antibodies

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Assumes birth position (head down)

Teratogens (Monsters) –

Any environmental agent that causes prenatal damage (leading to birth defects)

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Types – drugs, diseases, radiation, environmental pollutants

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Factors – dose, resilience (heredity), number of teratogens, gestational age at exposure (embryonic period worst)

Teratogens - Drugs 

Examples

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Thalidomide – 7000 infants affected

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Limbs, heart, ears, kidneys, genitals

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DES (diethylstilbestrol) – reproductive problems in adult children (cancer; abnormalities in reproductive organs)

Teratogens - Drugs –

Don’t take anything without consulting your obstetrician

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Examples

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Aspirin – may be associated with LBW, infant death, lower IQ, poor motor development

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Caffeine – LBW, miscarriage, irritable infants

Teratogens – Illegal Drugs – Cocaine – Heroin/methodone  Prematurity, LBW, breathing difficulties, physical defects, infant death, stressed and drug addicted – Marijuana  Smaller head size, disturbed sleep, inattention in infancy

Teratogens - tobacco 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 - Alcohol 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 - 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.

Environmental Teratogens    Radiation (Hiroshima, Nagasaki, Chernobyl) – Miscarriages, babies with underdeveloped brains, physical deformities, slow growth Mercury – 1950s Minamata, Japan – resulting brain damage in children Lead – prematurity, LBW, brain damage, physical defects  PCBs (insulators for electrical equipment) – lower intelligence

Teratogens – Infectious diseases

Rubella HIV/AIDS Genital herpes toxoplasmosis

Other Maternal Factors

Nutrition Emotional stress Maternal age & previous births

Prenatal Health Care

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 .

Approaches to Childbirth

 How much medical care/availability?

 Should it be natural or prepared?

 How about the epidural?

 How about a midwife (or a doula)?

The Birth Process

– Dilation and effacement (of the cervix)(Labor)  At transition a clear channel from the uterus to the vagina is formed (birth canal) – Birth of the baby (Delivery) 20-50 minutes – Delivery of the placenta (afterbirth) (5-10 minutes)

Birth Complications and Medical Interventions

– Anoxia – Breech position – Cerebral palsy – Fetal monitors – Medication (90-95% of births)  Analgesics, anesthetics – Cesarean delivery (30% of births)

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)  – Preterm babies – born early (35 or fewer weeks) may be weight appropriate – Small-for-date babies have more serious problems.

Apgar (1 & 5 minutes after birth)

 5 characteristics – Heart rate, respiratory effort, reflex irritability, muscle tone, color) – 0,1,or 2 points on each Total score – 7+, good physical condition – 4-6, baby requires assistance – 3-, infant in serious danger, requires emergency attention

The Newborn - Arousal

 Sleep 18-20 hours per day  50% is REM sleep  SIDS (Sudden Infant Death Syndrome)