Growth and Development Unit Five Prenatal Development

Fertilization: Conception. Humans have 23 pairs of chromosomes: one member of each pair was inherited from the mother and the other from the father.

Periods of Prenatal Development: The Germinal Period. The Embryonic Period. The Fetal Period.

The Germinal Period: First two weeks after conception. Zygote is created & attaches to uterine wall.

The Germinal Period: Cell division begins: Blastocyst inner layer of cells which later develop into embryo. Trophoblast outer layer of cells that provide nutrition & support for embryo. Implantation: attachment of zygote to uterine wall.

The Embryonic Period: From two to eight weeks following conception. Cell differentiation intensifies. Primary germ layers: Endoderm inner layer of cells which later form digestive & respiratory systems. Ectoderm outer layer of cells which becomes nervous system, sensory receptors &skin parts. Mesoderm middle layer of cells which becomes circulatory system, bones, muscles, excretory & reproductive systems

The Embryonic Period: Placenta: Life-support system consisting of group of tissues in which small blood vessels from mother & offspring intertwine.

The Embryonic Period: Placenta: Produce protein hormones: Human chorionic gonadotrophin (HCG)- 8-10 days past conception, is basis for pregnancy test. Progesterone. Estrogen. Human Placental Lactogen.

The Embryonic Period: Placenta: Sieve/filter – allows smaller particles through and holds back larger molecules. Passage of materials in either direction is effected by: Diffusion: gases, water, electrolytes. Facilitated transfer: glucose, amino acids, minerals. Pinocytosis: movement of minute particle

The Embryonic Period: Placenta: Mother transmits immunoglobulin G (IgG) to fetus providing limited passive immunity. Leakage: caused by membrane defect: may allow maternal and fetal blood mixing.

The Embryonic Period: Umbilical Cord: Life-support system, that connects baby to placenta. Contains two arteries & one vein (supported by mucoid material (wharton’s jelly) to prevent kinking and knotting) Transports oxygen and nutrients to fetus from the placenta and returns waste products from the fetus to the placenta. Contains NO pain receptors.

The Embryonic Period: Amniotic Fluid: Clear, yellowish fluid surrounding the developing fetus, enveloped by the amnion. Average amount 1000 ml. Having < 300ml – Oligohydramnios, associated with fetal renal abnormalities. Having > 2 L – Hydramnios, associated with GI and other malformations.

The Embryonic Period: Amniotic Fluid: Protects Fetus. Controls Temperature. Supports Symmetrical Growth. Prevents Adherence to amnion. Allows Movement.

The Fetal Period: From two months following conception to birth. Stages: First Trimester: From conception to 12 weeks. Features growth of arms, legs, brain & face; & is where heartbeat is detectable.

The Fetal Period: Second Trimester: Third Trimester: Between 12 to 24 weeks. Features development of skin, hair, & finger/toenails; & where movement such as thumb-sucking & hiccups are noticeable. Third Trimester: From 24 to 38 weeks & where increased activity. Periods of sleep & assumption of birth position are noticed.

The Fetal Period: Miscarriage and Abortion: Miscarriage: Is spontaneous abortion occurring before developing organism is mature enough to survive outside womb. Deliberate abortion: Is by choice & involves medical procedure. Selective abortion: Is legal in United States & that during first trimester, mother & her doctor can make choice without consulting others. Abortions occurring later than first trimester can have stipulations attached either legislatively or by courts.

The Fetal Period: Viability: Capability of fetus to survive outside uterus at the earliest gestational age - 22-24 weeks. Survival depends on: Maturity of fetal central nervous system. Maturity of lungs

1 Month: At the end of four weeks: Baby is 1/4 inch in length. Heart, digestive system, backbone and spinal cord begin to form. Placenta begins to develop. The single fertilized egg is now 10,000 times larger than size at conception.

Month 2: At the end of 8 weeks: Baby is 1-1/8 inches long. Heart is functioning. Eyes, nose, lips, tongue, ears and teeth are forming. Penis begins to appear in boys. Baby is moving, although the mother can not yet feel movement

Month 3: At the end of 12 weeks: Baby is 2 1/2 to 3 inches long. Weight is about 15 to 30 gram. Baby develops recognizable form. Nails start to develop and earlobes are formed.

Month 3: Arms, hands, fingers, legs, feet and toes are fully formed. Eyes are almost fully developed. Baby has developed most of his/her organs and tissues . Baby's heart rate can be heard at 10 weeks with a special instrument called a Doppler.

Month 4: At the end of 4 months: Baby is 6 1/2 to 7 inches long. Weight is about 170 to 200 grams. Baby is developing reflexes, such as sucking and swallowing and may begin sucking his/her thumb. Tooth buds are developing

Month 4: Sweat glands are forming on palms and soles . Fingers and toes are well defined. Sex is identifiable. Skin is bright pink, transparent and covered with soft, downy hair. Although recognizably human in appearance, the baby would not be able to survive outside the mother's body

Month 5: At the end of 5 months: Baby is 8 to 10 inches long. Weight is about 450 grams. Hair begins to grow on baby's head. Soft woolly hair called lanugo will cover its body. Some may remain until a week after birth, when it is shed.

Month 5: Mother begins to feel fetal movement. Internal organs are maturing. Eyebrows, eyelids and eyelashes appear.

Month 6: At the end of 6 months: Baby is 11 to 14 inches long. Weight is about 800 to 900 grams. Eyelids begin to part and eyes open sometimes for short periods of time. Skin is covered with protective coating called vernix. Baby is able to hiccup.

Month 7: At the end of 7 months: Baby is 14 to 16 inches long. Weight is about 1100 to 1600 grams. Taste buds have developed. Fat layers are forming. Organs are maturing. Skin is still wrinkled and red. If born at this time, baby will be considered a premature baby and require special care.

Month 8: At the end of 8 months: Baby is 16 1/2 to 18 inches long. Weight is about 1800 to 2700 grams. Overall growth is rapid this month. Tremendous brain growth occurs at this time. Most body organs are now developed with the exception of the lungs.

Month 8: Movements or "kicks" are strong enough to be visible from the outside. Kidneys are mature. Skin is less wrinkled. Fingernails now extend beyond fingertips.

Month 9: At the end of 9 months: Baby is 19 to 20 inches long. Weight is about 3200 to 3400 grams. The lungs are mature. Baby is now fully developed and can survive outside the mother's body. Skin is pink and smooth. Baby settles down lower in the abdomen in preparation for birth and may seem less active.

Body Systems' Development: Respiratory System: Terminal SAC period (necessary for surfactant production) - 24 Weeks to birth. Growth of primitive alveoli. Pulmonary surfactants produced which act as wetting agents that prevent alveolar walls from sticking. Insufficient surfactant – RDS.

Body Systems' Development: Cardiovascular System: 1st System to function. FHR 120-160/Min. Can hear FHR with Doppler at 10-12 Weeks. Fetal Circulation: Arteries in umbilical cord and fetal body carry deoxygenated blood. Vein in cord and those in fetal body carry oxygenated blood.

Body Systems' Development: Cardiovascular System: Fetal Circulation: Ductus venosus connects umbilical vein and inferior vena cava; bypassing portal circulation. Foramen Ovale allows blood to flow from right to left atrium, bypassing lungs. Ductus Arteriosus allows blood flow from pulmonary artery to aorta, bypassing fetal lungs

Body Systems' Development: Hepatic System: Liver functions 4-6 weeks. Full liver function after delivery. Musculoskeletal System: Bones and muscles develop by 4th week. Fontanels – areas where >2 bones meet. 7-8 Weeks arms & leg movements.

Body Systems' Development: Gastrointestinal System: Forms during 4th week. Middle portion of the intestine projects out into cord during 5th week. Returns during 10th week. If this does not occur- Omphalocele present at birth. Meconium – Dark green to black tarry waste accumulated in the fetal intestine near term.

Body Systems' Development: Renal System: Kidneys form in 5th week and begin to function 4 weeks later. Voiding into amniotic fluid. Low volume can show renal dysfunction. Renal malformation can be diagnosed in utero. GFR is low at birth.

Body Systems' Development: Neurological System: Formed from the ectoderm during the 3rd week. Fetal movement felt at 16-20 WKS (Quickening). Endocrine System: Thyroid gland 1st to develop. Insulin produced at 20 weeks

Body Systems' Development: Integumentary System: 7th week – Two layers of cells. Vernix caseosa –Protects skin. Lanugo – Fine hair. 10th week – Fingernails, toenails. Immune System: Passive immunity - FROM MOM. Active immunity - FROM FETUS

Teratology and Hazards To Prenatal Development: Teratogen: Agent that causes birth defect. Maternal Factors: Emanating from mother are: age, nutrition, emotional state and stress. Toxoplasmosis: Disease caused from parasite ingested from eating raw meat, or touching cat feces. Ectopic Pregnancy: Presence of developing embryo or fetus outside normal location in uterus.

Teratology and Hazards To Prenatal Development: Fetal Alcohol Syndrome: Cluster of abnormalities that appears in offspring of mothers who drink alcohol heavily during pregnancy. Paternal Factors: Emanating from father are: exposure to lead, radiation, pesticides, & petrochemicals. Also, fathers who have a diet low in vitamin C, often produce offspring with higher risks of birth defects & cancer.

Teratology and Hazards To Prenatal Development: Environmental Hazards: Pollutants, toxic wastes, chemicals & radiation can cause birth defects or adversely affect developing fetus. Recent research has shown that prolonged exposure by mothers to heat in saunas or hot tubs also endanger fetus. Fetal Surgery and Therapy is a recent practice in which surgical treatment is used to correct possible defects before permanent damage results after birth

Expectant Parents: Confirming the Pregnancy/Calculating the Due Date: Length of pregnancy is calculated from first day of woman’s last menstrual period, lasts an average of 280 days, or 40 weeks. Nagele’s Rule: Add 7 days to the first day of the last normal menstrual period, subtract 3 months and add 1 year. Example: 1st day of LMP=December 16, 2006 Add 7 days = Dec. 23, 2012 Subtract 3 months = Sept 23 2012 Add 1 year =Sept 23, 2013, estimated due date (EDD)

Expectant Parents: Preparation For Baby’s Birth: End of the pregnancy: Fetus descends into pelvic cavity signaling beginning of birthing process. End of the pregnancy: Is noticeable as baby’s head presses against mother’s pelvis & her cervix becomes softer & thinner.

Expectant Mother’s Nutrition, Weight Gain and Exercise: Nutrition and Weight Gain: Average weight gain is from 11 to 15 kilogram, at a rate of approximately 2 kilogram during first trimester followed by an average of 450 gram per week thereafter. Recommended daily allowance for all nutrients increases during pregnancy. Exercise: During pregnancy helps prevent constipation, conditions the body, & is associated with a more positive mental state.

Culture and Prenatal Care: How pregnancy is viewed culturally often determines quality of prenatal care. When viewed as a natural occurrence as opposed to medical condition, prenatal care is not priority. Culture influences health care practices during pregnancy such as in Mexican-American families where mothers & older women play essential role during prenatal period & birthing process.