Prenatal Development and Birth Chapter 3 Human Development

Prenatal Development and Birth Chapter 3 Human Development

The Study of Prenatal Development A model for the development of all subsequent periods (e. g. , stage-like changes) Understand how the developing organism can be affected by motherto-be’s health, habits, and lifestyle

Conception l l Conception occurs when a sperm cell penetrates and fertilizes an egg cell Successful conception depends on l l l ovaries releasing one healthy egg cell migrates most of the way down the fallopian tube One sperm must penetrate the ovum to form a zygote

Duration of Prenatal Periods 1. Germinal period (single-cell zygote morula blastocyst) l 2. Embryonic period (embryo) l 3. Conception to attachment (8 -10 days later) Attachment to end of 8 th week (when all major organs have taken primitive shape) Fetal period (fetus) l 9 th week (with first hardening of the bones) until birth

Germinal Period Fallopian tube Uterine wall

The Germinal Stage (first two weeks) The blastocyst is differentiated into three layers: the ectoderm, the endoderm, and the mesoderm. l The blastocyst moves down the fallopian tube into the uterus for implantation. l The embryonic stage begins with implantation, and the fully implanted blastocyst is referred to as the embryo. l

Germinal Period: Key Concepts l l l Cleavage: Mitotic division of zygote into multiple cells Heterochrony: Different parts of the organism develop at different rates Heterogeneity: Variability in levels of development of different parts of the organism at a given time

Germinal Period: Key Concepts l Epigenetic Hypothesis: Interactions between the cells and their environment generate the new cell forms and emergence of body organs

Germinal Period: Blastocyst Inner cell mass will eventually become the embryo, while the trophoblast will develop into membranes (e. g. , amnion, chorion placenta) that will protect and support the embryo.

Embryonic Stage (3 rd through 8 th weeks) l Growth in the embryonic and fetal stages follows a cephalocaudal (head-to-tail) pattern and a proximodistal (near-to-far) pattern. l The head, blood vessels, heart, and most vital organs begin to develop before the arms, legs, hands, and feet.

Embryonic stage § § § The placenta forms as an area of the uterine wall through which oxygen and nutrients reach the fetus. The umbilical cord connects the embryo to the placenta and provides nutrients and carries away waste products. The amniotic sac surrounds the embryo and protects it.

Embryonic Period l Begins with implantation and lasts for about 6 weeks l l l Basic organs formed; sexual differentiation occurs Organism begins to respond to direct stimulation (e. g. , will turn its head in response to a light touch around the mouth) Developmental patterns l l Cephalocaudal: Proceeds from head down Proximodistal: From middle of organism out to the periphery

Fetal Period Begins with skeletal ossification From week 8/9 until birth From 1¼ 20 inches From 8 3250 grams

Fetal Period Fetus at approx. 9 weeks

Fetal Stage (9 th to birth) The fetal stage is marked by the development of the first bone cells. The embryo is now called the fetus. l By the third month, the fetus is able to move its head, legs, and feet. By the fourth month, the mother may feel quickening, or fetal movement. l The beginning of the seventh month is considered the age of viability. l At the end of nine months, the fetus weighs on average 7. 5 pounds and is almost 20 inches long. l

Fetal Development l l l l 10 th week: Intestines in place; breathing and jawopening movements 12 th week: Sexual characteristics; well-defined neck; sucking and swallowing movements 16 th week: Head erect and lower limbs well-developed 5 th month: As many nerve cells as it will ever have 7 th month: Eyes open and lungs capable of breathing 8 th month: Many folds of the brain present 9 th month: Brain more convoluted Fetus doubles in weight in final weeks before birth

Prenatal Development of the Brain

Fetal Sensory Capacities l Sensing motion l l Vision l l Sense of balance at 5 months Responds to light (i. e. , heart rate changes, increased movement) at 26 weeks Sound l l Responds at 5 -6 months Can discriminate outside sounds, but hears mother’s voice best (i. e. , changes in heart rate)

Maternal Conditions: Attitudes & Stress l l Presence of a sympathetic mate and other supportive family members, adequate housing, and steady employment – factors that give a woman a basic sense of security – appear to enhance the prospects for a healthy baby (Thompson, 1990) Psychological stress during pregnancy is associated with premature delivery and low birth weight (Hedegaard, 1993) Prolonged anxiety just before or during pregnancy increases the likelihood of medical complications. Emotional stress is related to spontaneous abortion as well as to labor and birthing problems.

Maternal diet and nutrition Poor nutrition leads to specific physical deformities and increased risk for prematurity and infant mortality; later nutritional deprivation leads to a reduced number of brain cells. l Pregnant women should eat between two hundred and one thousand calories more per day, adding mainly carbohydrates and protein. l

Maternal Conditions: Nutrition Rotterdam, Holland Spontaneous abortions, stillbirths, malformations, and deaths at birth increased markedly.

Prenatal health care Adequate early prenatal health care is critical to infant and maternal health. l There are racial differences in adequacy of care. l Special programs have been implemented in communities to help high-risk mothers. l

Maternal Conditions: SES

Teratogens: Drugs l l l Prescription: Thalidomide (nausea), Valium (tranquilizer), Accutane (acne), streptomycin & tetracycline (antibiotics), artificial hormones Caffeine: Increased rate of spontaneous abortion and low birth weight Marijuana: Low birth weight, premature delivery; infants startle more readily, have tremors, and experience sleep cycle problems Cocaine: More likely to be stillborn or premature, have low birth weights, have strokes, have birth defects; infants more irritable, uncoordinated, slow learners Methadone & Heroin: Born addicted; likely to be premature, underweight, vulnerable to respiratory illness, tremors, irritable; infants have difficulty attending, poor motor control

Teratogens: Alcohol Fetal Alcohol Syndrome Abnormally small head, underdeveloped brain, eye abnormalities, congenital heart disease, joint anomalies, malformations of the face Most serious damage from alcohol caused in first weeks of pregnancy Are evident in their inability to pay attention or maintain attention

Teratogens: Alcohol Normal Brain Fetal Alcohol Syndrome Brain

Teratogens: Smoking Increase in rate of spontaneous abortion, stillbirth, and neonatal death Nicotine results in abnormal growth of the placenta Similar effects from cigarette smoke of others

Tobacco l l Nicotine and carbon monoxide interfere with fetal oxygen supply Smoking is associated with low birth weight, spontaneous abortion, higher infant mortality, and poor postnatal adjustment

Teratogens: Infections, etc l l l Rubella (German measles): Can cause a syndrome of congenital heart disease, cataracts, deafness, and mental retardation in more than half of all babies born to mothers who suffer from the disease during the first 12 weeks of pregnancy Syphilis and gonorrhea. Blindness, jaundice, anemia, pneumonia, skin rash, early death. Silver nitrate in the eyes. Genital herpes. (1) Disease of skin and mucous membranes, or (2) blindness, permanent brain damage, seizures, and developmental delay.

Teratogens: Infections, etc l l l Cytomegalovirus (CMV). High risk for infants; jaundice, microcephaly, deafness, and eye problems. Toxoplasmosis. Parasite from uncooked meat and cat feces. Low birth weight, enlarged liver and spleen, microcephaly, anemia, and calcifications in the brain. AIDS: Approximately 30% of the babies born to mothers who test positive for the AIDS virus acquire this disease

Teratogens: Critical Periods Most vulnerable when first forming

Teratogenic Principles 1. 2. 3. 4. 5. 6. The susceptibility of the organism depends on the stage of its development. A teratogen’s effects are likely to be specific to a particular organ. Individual organisms vary in their susceptibility to teratogens. The physiological state of the mother influences the impact of a teratogen. The greater the concentration of a teratogenic agent, the greater the risk. Teratogens that adversely affect the developing organism may affect the mother little or not at all.

Birth: The First Bio-Social-Behavioral Shift

Death Rates Post Delivery (USA)

The Birth Episode l Birth l After about thirty-eight weeks in the womb, the baby is considered "full term, " or ready for birth. Fetal presentation refers to the body part closest to the mother's cervix. There are two types of presentation: A. Cephalic (normal), and B. Breech. A B

Stages of labor § 1. During the last weeks of pregnancy, it is common for the mother to experience false labor, or Braxton-Hicks contractions. § 2. The first stage of labor usually begins with relatively mild contractions, leading to stronger contractions and the dilation of the cervix to accommodate the baby's head (10 centimeters).

Stages of labor 3. Toward the end of the first stage, which may take from eight to twenty-four hours, a period of transition begins, and the baby's head begins to move through the birth canal. 4. The second stage of labor is from complete dilation of the cervix to birth, lasting about one to one and one-half hours. 5. During the third stage of labor, which lasts only a few minutes, the afterbirth (consisting of the placenta and umbilical cord) is expelled

Childbirth Settings and Methods Traditionally, childbirth was attended by a midwife and was seen as a natural process. With the advent of modern technology, births increasingly took place in medical settings. This resulted in decreased mortality rates, but birth was now seen as a medical event controlled by physicians.

§ Hospital births. Birthing rooms are becoming more popular in hospitals. § Non-hospital settings § Freestanding birth centers are non-hospital facilities that provide family centered maternity care. § Birth centers have lower rates of Caesarean sections. § Home births are another alternative for pregnancies predetermined to be low risk. § Prepared childbirth. Lamaze Methods of prepared childbirth help parents rehearse the sensations of labor.

Medicinal Aids to Birth l Despite good psychological preparation, the mother may experience considerable pain, which can be made bearable through pain-reducing drugs such as narcotics or other sedatives. § § The most common anesthetics are epidural and spinal, which allow the mother to remain awake and alert during birth. A general or local anesthetic delays the recovery of the mother as well as the bonding between mother and child.

Problems During Labor and Delivery (1 of 2) Faulty power is the failure of the uterus to contract strongly enough to make labor progress to an actual delivery. Induced labor can be stimulated by the hormone oxytocin. l A faulty passageway condition occurs when the placenta develops so close to the cervix that it blocks the baby's passage down the birth canal during labor. This condition is called placenta previa. l

Problems with Labor and Delivery (2 of 2) § A faulty passenger condition occurs when problems exist with the baby's position or size. Usually babies enter the birth canal head first, but occasionally one turns in the wrong direction during contractions. Forceps sometimes are used to remedy the situation. § In a Caesarean section, the mother receives a general anesthetic and the baby is removed surgically. Techniques for this surgery have improved; however, a common criticism is that too many Caesareans are performed.

Assessing Viability Physical condition: Apgar Scale… Neurological condition: Brazelton Neonatal Assessment Scale… Good guides for determining necessity of medical intervention and normal development. Not so useful for predicting later intelligence or personality.

Apgar Scoring System Rating (at 1 & 5 minutes after birth) Vital Sign 0 1 2 Heart rate Absent Slow (<100) Over 100 Respiratory effort Absent Slow, irregular Good, crying Muscle tone Flaccid Some flexion of extremities Active motion Reflex responsivity No response Grimace Vigorous cry Color Blue, pale Body pink, extremities blue Completely pink

Brazelton Scale l Includes tests of infant reflexes, motor capacities, muscle tone, capacity for responding to objects and people, capacity to control own behavior, attention l l l Orientation to animate objects (visual/auditory) Pull-to-sit (e. g. , try to right his head) Cuddliness (e. g. , resist, passive, tries to cuddle) Defensive movements (e. g. , try to remove cloth from face) Self-quieting activity (e. g. , suck thumb, look around)

Premature Birth Born before 37 th week More likely in twins, very young mothers, women who smoke or are undernourished

Consequences of Premature Birth l l l Immaturity of the lungs (leading cause of death among preterm infants), as well as of their digestive and immune systems Premature babies who are of normal size for their gestational age stand a good chance of catching up with full-term babies However, some children born prematurely have problems with maintaining attention and with visual-motor coordination when they are school age

Low Birth Weight l l Typical weight at birth: 7 to 7½ lbs. Causes of fetal growth retardation l l Multiple births; intrauterine infections; placenta abnormalities; maternal smoking, use of narcotics, or malnutrition Developmental consequences l l Two-thirds of deaths that occur in the period immediately following birth are among low-birth-weight infants 3 x more likely to have neurologically-based developmental handicaps Decrease in intellectual capacities in childhood However, babies who are raised in good SES circumstance with an intact family and a mother with good education are less likely to suffer negative effects from their condition at birth than children raised without these benefits