Prenatal Develepment & Birth

Prenatal Development & Birth Chapter Three

Conception & Genetics When does life begin? Process of Conception: Every 28 days egg is released, which contains 23 chromosomes Gametes – cells that have only 23 chromosomes. Rx indicates that only about half of all conceptions are likely to survive to birth. What are some reasons for this large number of fertilized eggs not surviving? Male gamete + female gamete = zygote

Conception Two Types of Chromosomes: 22 of the pairs of chromosomes are called autosomes Sex chromosomes = X or Y Female has two X chromosomes (XX) Male has one X and one Y Gender of a child is determined by the sex chromosome from the sperm (because mom only has X chromosomes) Chromosomes are comprised of DNA (deoxyribonucleic acid) that is further subdivided into genes.

Monozygotic Twins Aka= identical twins A single egg is fertilized to form one zygote which then divides into two separate embryos. Odds of having identical twins are about 4 in 1,000 Same sex (gender)

Dizygotic Twins Aka = fraternal twins Two eggs are fertilized by two separate sperm. Same sex or opposite sex Number of multiple births has increased 65% over last 25 years Women 35+ more likely to conceive twins & other multiples Women 35+ are more likely to be treated with fertility drugs

Genetics Genotype – specific genetic material on an indiv’s chromosomes. Phenotype – the observed characteristic of the indiv (brown eyes; blonde hair)

DOMINANT AND RECESSIVE CHARACTERISTICS Characteristics in the left-hand column dominate over those characteristics listed in the right-hand column . * sex-linked characteristic no dimples attached earlobes no freckles thin lips Susceptibility to poison ivy Congenital deafness Hemophilia albinism dimples unattached earlobes freckles broad lips Immunity to poison ivy Normal hearing Normal blood clotting Normal pigmented skin facial features Other blonde, light, red hair red hair straight hair baldness* normal hairline dark hair non-red hair curly hair full head of hair widow's peak hair normal vision nearsightedness night blindness color blindness* farsightedness normal vision normal vision normal vision vision grey, green, hazel, blue eyes brown eyes eye coloring RECESSIVE TRAITS DOMINANT TRAITS

Dominant-Recessive Genes Simplest set of genetic rules = dominant-recessive pattern a single dominant gene strongly influences phenotype Because inherit one chromosome from each parent, our genetic instructions either= Homozygous (the same) Heterozygous (different) Homozygous for curly hair if received a gene from each parent for curly hair. Heterozygous if received a gene for curly hair from mom and a gene for straight hair from dad.

Polygenic Inheritance Many genes influence the phenotype. controlled by more than one gene, ie. height, weight, hair color, skin color (basically anything dealing with color).

Multi-Factorial Traits Physical traits influenced by both genes and environment. Height is an example: If a child is ill, poorly nourished, or emotionally neglected, s/he may be smaller than others her/his age. Psychological traits (intelligence, personality) influenced by both nature and nurture (multi-factorial)

Nine months? Pregnancy begins when the zygote (male gamete + female gamete) implants itself in the lining of the woman’s uterus. Zygote send chemical messages for menstruation to stop.

Twenty weeks… the uterus can be felt at the level of your bellybutton As a result, the pelvic colon and small intestines are crowded upward and backward.

The end! 40 weeks Common discomforts you may experience during the last weeks of pregnancy are frequent urination, increased constipation, edema (water retention), and aching of the legs

Prenatal Development Developmental Principles: Cephalocaudal pattern – causes dev’t to proceed from the head down. Proximodistal pattern – causes dev’t to happen in an orderly way from the center of the body outward to the extremities. Three Stages of Prenatal Dev’t: Germinal Stage 2. Embryonic Stage 3. Fetal Stage

Germinal Stage First two weeks of gestation, from conception to implantation = germinal stage During first 24-36 hours after conception cell division begins Cells are alike until @ 4 days after conception; they form a hollow sphere with two layers = blastocyst . Placenta = organ that allows oxygen, nutrients and other substances to be transferred between mom and baby’s blood. (Brings mother’s and baby’s blood close to one another without allowing them to mix.) Blastocyst’s inner cells begin to specialize Umbilical cord – connects the embryo to the placenta Aminion – fluid-filled sac in which baby floats

Embryonic Stage Begins when implantation is complete (@ 2 nd week) Ends at week 8 Embryo’s cells start to specialize to form body’s organs (aka: organogenesis )

Fetal Stage Beginning at week 8 and ending at birth Weight increases from one-fourth ounce to 7-8 pounds Height increase from one inch to 20 inches Nervous system dev’t Viability = baby’s ability to live outside the womb (@ 22 weeks)

Gender Differences Male fetuses tend to be more physically active than female fetuses Male embryo secretes the male hormone testosterone Female fetuses tend to be more sensitive to external stimulation and advance more rapidly in skeletal dev’t Boys are more vulnerable to prenatal probs (spontaneous miscarriage; birth defects)

Prenatal Behavior 25 th week, fetus responds to sounds and vibrations with heart rate changes, head turns and body movements. Neonates appear to remember stimuli to which they were exposed prenatally—their mother’s heartbeat, the odor of amniotic fluid… Very active fetuses tend to become children who are very active Fetuses who are less active than “average” are more likely to be developmentally delayed.

Genetic Disorders Autosomal Dx Caused by genes located on the autosomes. i.e., phenylketonuria (PKU) = involves a recessive gene that causes a baby to have prob’s digesting the amino acid phenylalanine. Can cause MR as the toxins build up in baby’s brain. More likely to occur in Caucusian babies. Sickle-cell disease = recessive dx that causes red blood cell deformities. Blood can’t carry enough oxygen to keep the body’s tissues healthy. More common in West African and African-American infants. Huntington’s disease = caused by dominant genes and not usually diagnosed until adulthood. Causes the brain to deteriorate and affects psychological and motor functions.

Genetic Disorders Sex-Linked Dx’s Most sex-linked dx’s are caused by recessive genes i.e., red-green color blindness = people have difficulty distinguishing between the colors red and green when they are next to each other. Hemophilia = the blood lacks the chemical components which cause the blood to clot. Fragile-X syndrome = person has a “fragile” or damaged spot on the X chromosome. Can cause MR that becomes progressively worse as children age. What if parents find out their baby has a genetic dx? Should this information influence their decisions?

Chromosomal Errors Chromosomal errors = Probs that occur when a child has too few or too many chromosomes Trisomies = a condition in which a child has three copies of a specific autosome. Most common is trisomy 21 or Down syndrome (3 copies of chromosome 21) Sex-Chromosome Anomalies = anomalies associated with the sex chromosomes Klinefelter’s syndrome – XXY pattern. Affected boys usually look normal but have underdeveloped testes and a sparsity of sperm. At puberty, they experience both male and female changes.

Prenatal Influences on Development Environmental factors – Teratogens – environmental stimuli harmful to developing fetus Diseases during pregnancy – any disease that can cross the placenta German measles = minor effects on mother, major effects on fetus (blindness, deafness, heart disease) Genital herpes & AIDS= can cross placenta Drugs – legal & illegal Caffeine = can slow fetal growth & contribute to premature birth FAS = abnormally small head, irritability, hyperactivity & retarded motor development and cognitive development

Other Maternal Influences on Prenatal Development Diet Inadequate nutrition may result in premature birth and low birth weight Folic acid – need adequate amounts; inadequate amounts can result in diseases such as spina bifida Age Societal shift = older mothers Older mothers = higher risk for genetic abnormalities, miscarriage & stillbirth What about older fathers? Maternal Emotions Studies show extreme maternal stress is associated with low birth weight and premature births. Environmental Hazards Lead, mercury, x-rays Effects may include mental disability, retarded growth, impaired memory and verbal skill, and leukemia.

Prenatal Diagnosis and Treatment Genetic Counseling Helps to assess the chances of inherited disorders. Prenatal Diagnosis Ultrasound is the use of soundwaves to produce a picture of the fetus. Amniocentesis allows the taking of a sample of the amniotic fluid. Chorionic Villus Sampling (CVS) is taken from the placenta and can be done earlier than amniocentesis.

Prenatal Diagnosis and Treatment (cont.) Fetal Medicine Administering medicine to the fetus. Fetal Surgery to correct spina bifida and circulatory problems. Genetic Engineering involves replacing defective genes with synthetic normal genes.

Birth: The Final Push Labor and Delivery What are the different phases of labor and delivery? What are “natural” ways of coping with the pain of childbirth? Is childbirth at home safe? What are some complications that can occur during birth?

Labor and Delivery Stages of Labor Stage 1 lasts 12-24 hours for the first birth and includes contractions and the enlargement of the cervix to approximately 10 centimeters. Stage 2 includes the actual birth of the baby and lasts about an hour. Stage 3 lasts a few minutes and involves expelling of the placenta.

Labor and Delivery Approaches to Childbirth Childbirth Classes Explains what happens during pregnancy and delivery. Teaches techniques to manage the pain of childbirth. The emphasis is on natural methods, relaxation, and coaching. Studies show that mothers who attend childbirth classes typically use less medication.

Labor and Delivery Approaches to Childbirth Birthing Alternatives Home Births Less Expensive Parents have more control over the conditions Birth problems are no more common at home than at the hospital when pregnancy has been problem-free. Birthing Centers More home-like than hospitals, but in a clinic setting independent of hospitals.

Labor and Delivery: Birth Complications Hypoxia, or inadequate blood and oxygen to baby. Complications may result in cesarean section (C-section) Births before the 36th week are called premature or preterm. Babies weighing less than 5.5 pounds have low birth weight. Babies weighing less than 3.3 pounds have very low birth weight. Below 2.2 pounds is called extremely low birth weight.

Labor and Delivery Infant Mortality Infant Mortality is the number of infants out of 1,000 births that die before the age of 1 year. U.S. mortality rate is about 1%, or 9 of 1000. 15 industrialized nations have lower infant mortality than U.S. Possible factors include low birth weight resulting from a lack of free or inexpensive prenatal care and fewer paid leaves of absence for pregnant women.

Apgar Test Pink all over Body pink w/blue extremities Blue or pale body/ Extremities Body color Active crying Some contortions and grimacing No facial expressions Reflex Irritability Good flexion and active motion Some flexion of extremities Limb and flaccid Muscle Tone Good respiration normal crying Slow and irregular No breathing for 1 min Respiratory Effort 100-140 beat/min <100 beats/min Absent Heart Rate 2 1 0 Sign

Prenatal Develepment & Birth

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Prenatal Develepment & Birth