Lecture 7: Prenatal Development

Question 1

Conception

Answer 1

Results from the union of two gametes (reproductive cells), the egg and the sperm

Gametes are produced through a specialised cell division, meiosis, which results in each gamete having only half the genetic material of all other norma, cells in the body

Fertilisation (fusion of the egg and the sperm) typically takes place in the fallopian tubes

Question 2

The Zygote and prenatal development

Answer 2

The fertilised egg, or zygote, has a full complement of human genetic material, half from each parent

Marks the beginning of the three periods of prenatal development

1. Germinal (conception- 2 weeks)
2. Embryonic (3rd- 8th week)
3. Fetal (9th week-birth)

Question 3

Germinal

Answer 3

Conception to two weeks/ implantation

Begins with conception and lasts until the zygote becomes implanted in the uterine wall

Rapid cell division takes place- as early as 12 hours after fertilisation

Mitosis- zygote doubles its number of cells roughly twice a day

Question 4

Embryonic

Answer 4

Implantation to 8 weeks

Following implantation, major development occurs in all the organs and systems of the body. Development takes place through the processes of:

Cell division: results in proliferation of cells

Cell migration: movement of cells from point of origin to other locations in embryo

Cell differentiation: transformation of stem cells into roughly 350 different types of specialised cell

Cell death: selective death of certain cells (apoptosis)

Question 5

The embryo

Answer 5

After implantation, the inner cell mass becomes the embryo and the rest of the cells develop into its support system

The neural tube is a U-shaped groove formed from the top layer of differentiated cells in the embryo
It eventually becomes the brain and spinal cord.

Question 6

The embryo and its support systems

Answer 6

Placenta: semi-permeable, permits the exchange of materials between the bloodstream of the foetus and that of the mother

Umbilical cord- the tube that contains the blood vessels that travel from the placenta to the developing organism and back again

Question 7

Prenatal development- Foetal (9 weeks- birth)

Answer 7

Continued development of physical structures and rapid growth of the body
Receives antibodies from mother in last month (particularly) of pregnancy
Increasing levels of behaviour, sensory experience, and learning

Question 8

Protecting the foetus

Answer 8

The placenta membrane is a barrier against some, but not all toxins and infectious agents

The amniotic sac, a membrane filled with fluid in which the foetus floats, provides a protective buffer for the foetus

Also helps regulate temperature

Question 9

Foetal behaviour - movement

Answer 9

Movement
Spontaneous movement from around 5 weeks

Hiccups at 7 weeks

Initially jerky movements becoming more integrated
After around 18-19 weeks- most arm movements are hand to mouth

Question 10

movement 12 weeks after gestation

Answer 10

By 12 weeks after gestation, most of the movements that will be present at birth have appeared

Prenatal to postnatal continuity

Swallowing amniotic fluid promotes the normal development of the palate and aids in the maturation of the digestive system

Movement of the chest wall and pulling in and expelling small amounts of amniotic fluid help the respiratory system become functional

Question 11

Foetal rest-activity cycles

Answer 11

Become stable during the second half of pregnancy

Circadian rhythms are also apparent

Near the end of the pregnancy, the foetus’s sleep and wake are similar to those of the newborn

Question 12

Foetal sensation (perception)

Answer 12

The sensory structures are present relatively early in prenatal development and play a vital role in foetal development and learning

The foetus experiences tactile stimulation as a result of its own activity, and tastes and smells the amniotic fluid

The foetus typically responds to sounds from at least the 6th month of gestation

Question 13

Foetal visual experiences

Answer 13

Was previously thought to be negligible, but recent evidence shows preference for “faces” in the foetus (Reid et al ., 2017) suggesting postnatal exposure is not necessary

Question 14

Teratogens

Answer 14

Environmental agents that have the potential to cause harm during prenatal development

Timing is a crucial factor in the severity of the effects of potentially harmful agents

Many agents cause damage only if exposure occurs during a sensitive period in development

Question 15

Exposure to teratogens

Answer 15

Amount and length of exposure to the teratogen is also important. Most teratogens show a dose-response relation

Increases in exposure to potential teratogens are associated with greater probabilities of foetal defects and with more severe problems

Individual differences also influence the effects of teratogens (often harmless but gene-dependent)

Question 16

How is identifying teratogens and their effects made difficult

Answer 16

Their combination

(a mother with substance-abuse problems may be exposed to more than one harmful substance, also have poorer diet, polluted environment)

Sleeper effects in which the impact of a given agent may not be apparent for many years

E.g., the minamata disease of the 1950s

Hormone DES to prevent miscarriage

Question 17

Environmental hazards to foetus or newborn

Answer 17

Drugs: alcohol, cocaine, heroin

Environmental pollutants: lead, mercury, PCBs

Maternal disease: AIDS, chicken pox, chlamydia

Question 18

Teratogens - alcohol

Answer 18

Most common human teratogen (Ramadross, 2008)- leading cause of preventable foetal brain injury

Crosses the placenta, also found in amniotic fluid

Advice given to mothers changes regularly

Maternal alcohol abuse can lead to foetal alcohol syndrome (FAS), which is associated is associated with delays in cognitive development, facial deformity, and other problems

Question 19

Teratogens- cigarette smoking

Answer 19

Cigarette smoking during pregnancy is linked to reduced growth and low birth weight (Reduced oxygen)

Effects can be reduced immediately by stopping smoking

Cigarette smoking has also been linked to SIDS (sudden infant death syndrome), also the ultimate causes of SIDS are still unknown

E-cigs (vaping): many pregnant women believe that e-cigarettes are healthier for their unborn baby than tobacco (e.g., Wagner et al., 2017), but nicotine itself is a risk factor for foetal cardiac, respiratory, and nervous system development

Question 20

Teratogens- illegal drugs

Answer 20

Marijuana
- Doubles risk of still born birth
- memory , learning, attention, impulsivity

Cocaine
- Foetal growth retardation, premature birth, attentional/arousal problems
- Withdrawal

Question 21

Teratogens- other hazards

Answer 21

Environmental hazards
E.g., pesticides, herbicides, pollutants (e.g., heavy metals, car exhausts) etc.
Memory, learning, visual skills

Occupational hazards
farmers , factory workers, chemists, nurses
Increased physical labour, noise, being around people with illnesses

Nutrition
Folic acid: spina bifida
Inadequate nutrients

Disease
E.g., Rubella, STIs (herpes, HIV)
Zika

Age
older/ younger mothers at greater risk of negative outcomes

Question 22

Newborn infant interacting with the environment

Answer 22

state : The infant’s level of arousal and engagement in the environment

Ranges from deep sleep to intense activity

Is an important influence in the newborns exploration of the world

Question 23

Six stages of arousal in newborns

Answer 23

most to least time:
Quiet sleep- 8hrs
Active sleep- 8hrs
Active awake- 2.5hrs
Alert awake- 2.5 hrs
Drowsing- 1hr

Question 24

Newborns and sleep

Answer 24

Newborns sleep twice as much as young adults. The pattern of two different sleep states changes dramatically

Question 25

REM Sleep

Answer 25

REM (rapid eye movement) sleep: as active sleep state associated with dreaming in adults and is characterised by quick, jerky eye movements under closed lids

REM sleep constitutes fully 50% of a newborn’s total sleep time and declines rapidly to only 20% by 3 or 4 years of age

According to the autostimulation theory, brain activity during REM sleep in the foetus and newborn makes up for natural deprivation of external stimuli and facilitates the early development of the visual system

Question 26

NON-REM sleep

Answer 26

Non-REM sleep: A quiet or deep sleep state characterised by the absence of motor activity or eye movements and by regular, slow brain waves, breathing, and heart rate

Question 27

Crying

Answer 27

Early in infancy, crying reflects discomfort or frustration
Crying gradually becomes more of a communicative act

With experience, parents become better at interpreting the characteristics of the cry itself

Question 28

Infant mortality

Answer 28

Death during the first year after birth
(infant mortality) has become a relatively rare event in the western industrialised world

In the United States in 2015, infant mortality rates were 5.87 deaths per 1000 live births (high compared with other industrialised nations)

African-American infants are more than twice as likely to die before their first birthday as Euro-American babies

Poverty and lack of health insurance are associated with high rates of infant mortality

Question 29

Low birth weight infants

Answer 29

Infants weighing less than 5.5 pounds (2,500 grams) are considered to be of low birth weight (LBW)

LBW infants born at or before 37 weeks after conception are described as premature

Other LBW infants are referred to as small for gestation age (SGA) when their birth weight is substantially less than the norm for their gestational age

Question 30

LBW Infants

Answer 30

As a group, LBW babies experience more medical complications, have more developmental difficulties, and present special challenges for parents

However the majority of LBW babies turn out quite well

Extensive parent contact and more touch for infants in neonatal intensive care are widely used interventions