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Development Patterns• Cephalocaudal

• Proximal-distal

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Embryonic Development

• Conception-2 weeks: ZygoteZygote– about half survive

this stage– rapid cell

differentiation– ~ 10 days outer

part of zygote attaches to uterine wall; placenta develops

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Embryonic Development

• First month (0- 4 weeks after conception)– Wt. is 400mg, Ht. is 1 cm.– Limb buds are present– Organs start to form– Heart pumps blood– C-shaped body.– Head is 1/3 of entire

body.

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• Second month (5- 8 weeks)– Formation of head and

facial features.– Skeleton is visible.– Organogenesis is

complete.– Eyes formed and open– Extremities have

developed (some movements).

– Wt 1 gm, Ht is 2.5cm.

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• Third month (9- 12 weeks)– Teeth begin to appear.– Kidneys begin to function– Some respiratory-like

movements.– Begin to swallow amniotic

fluid.– Grasp, sucking, blinking and

withdrawal reflexes present.– Gender easily distinguished– Weight 30 gm.– Sleeping and activity patterns

are distinguishable

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• Fourth month (13- 16 weeks)– Much spontaneous

movements.– Moro reflex present.– Rapid skeletal development.– Meconium present.– Downy hair (lanugo)

appears on body.– Weight 120 gm.

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Fifth month (17- 20 weeks)

• Mother usually feels movement (quickening)

• Vernix caseosa appears.• Eyebrows and hair appear.• Strong grasp reflex present.• Permanent teeth buds

appear.• Brown fat is formed.• Heart sound can be heard

with stethoscope.• Weight 360gm.

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• Sixth month (21- 24 weeks)– Extra uterine life possible.– Begin to produce

surfactant.– Skin has red wrinkled

appearance.– Alternative periods of sleep

and activity.– May respond to external

sounds.– May try to find comfortable

position.– Weight 720 gm.

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• Seventh month (25- 28 weeks):– Respiratory and

central nervous system sufficiently developed.

– Eye lids open and close spontaneously.

– Assumes head-down position in uterus.

– Weight 1200 gm.

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• Eighth month (29- 32 weeks):– Begins to store fat and

minerals.– Testes descend into scrotal

sac.– Lanugo begins to disappear

from face.– Skin begins to lose reddish

color.– Weight 2000 gm.

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• Ninth month (33- 36 weeks):– Increased iron storage

by liver.– Increased

development of lungs.– May become more or

less active due to space tightness.

– Weight 2800 gm.

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• Tenth month (37- 40 weeks):– High absorption of

maternal hormones.

– Continued storage of fat and minerals.

– Ready for birth.

– Weight 3200 gm.

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• Chromosomal factors

• Developmental factors– Teratogens– Drugs– Maternal Nutrition– Maternal disease– Stress– Fetal factors

Factors that affect development

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Teratology

• Teratogens– Any agent that causes a birth defect– After Greek “monster creating”

• Variables affecting influence of teratogens– Timing of exposure– Intensity & duration of exposure– Number of harmful influences present– Biogenetic vulnerability of mother & infant

sensitivity

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Most Most serious serious damage damage from from

teratogens teratogens in first in first 2-8 wks2-8 wks

Zygote Embryonic period (wks) Fetal Period (wks)

Period of susceptibility to functional defects

Period of susceptibility to structural defects

Fig. 4.4

1 2 3 4 5 6 7 8 9 16 32 38

Teratogens and Timing of Their Effects on Prenatal Development

Central nervous system Heart

ArmsEyes

Legs Ears

TeethPalate

External genitalia

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• TeratogensTeratogens: – Viruses:

• Rubella- most serious if exposed between 4-8 weeks; later prenatal exposure seldom life-threatening (congenital deafness common)

• HIV- 20-50% may pass on virus prenatally or during delivery

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Prescription Drugs• Thalidomide – sedative used in early 1960s

– Infants with severe defects• Diethylstibestrol (DES) – used to prevent

miscarriages (cancer of reproductive system)– Abnormalities appeared in adulthood

• Antibiotics (streptomycin, tetracycline)• Some depressants• Certain hormones (progestin, synthetic

estrogen)• Accutane( used to treat acne) • Coffee

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Illegal Drugs

• Cocaine - reduced birth weight, length, and head circumference; impaired motor development; poor attentional skills

• Marijuana - increased tremors and startles among newborns; poorer verbal and memory development

• Heroin – addiction & withdrawal symptoms including tremors, irritability, abnormal crying, disturbed sleep, impaired motor control; attention deficits

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Environmental Hazards

• Radiation: nuclear environments, X-rays, computer monitors

• Chemicals: carbon monoxide, mercury, lead, pesticides.

• Heat: saunas, hot tubs

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• Fetal alcohol effects (FAE); more severe form (FAS)

• Fetal Alcohol Syndrome (FAS)– Low birth weight; lack of responsiveness– Facial deformities; defective limbs, face, and heart– Below average intelligence, with some cases of

mental retardation– Adults with FAS found to have a high incidence of

mental disorders, such as depression or anxiety

Alcohol and Pregnancy

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• Higher fetal and neonatal deaths

• Higher incidence of preterm births and lower birth weights

• Related to poorer language development & cognitive development by age 4

• Respiratory problems and SIDS are more common

Nicotine

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• Diet Pills• Aspirin ( baby Aspirin is

prescribed for problem in the placenta)

• Caffeine– Small increase in the risks for

spontaneous abortion and low birth weight occurs for pregnant women consuming >150 mg caffeine per day.

Nonprescription Drugs

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Maternal Age

• Adolescence

• Older mothers

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Domestic Violence

• 7-8% pregnant women are beaten

• Twice the miscarriage rates

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• Important factors of nutritional status are– total number of calories– levels of protein, vitamins, and minerals– folic acid - linked with neural tube defects,

such as spina bifida

• Poor diet linked to infant mortality & prematurity

• Malnourished infants have significantly reduced number of brain cells

Nutrition

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• Severe or prolonged stress increases medical complications & infant abnormalities

• Linked to spontaneous abortion, difficult labor, premature birth, low birth weight, newborn respiratory difficulties

Effects of Stress on Pregnancy

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• Exposure to lead, radiation, certain pesticides, and petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

• Diet low in vitamin C, increases risk of birth defects and cancer.

• Connection between cocaine use in fathers and birth defects.

• Fathers’ smoking during pregnancy may lead to lower birth weight and potential for their offspring developing cancer.

• Older fathers have higher risk for birth defects (e.g., Down syndrome & dwarfism.

Paternal Factors