Fetal Development and Genetics CHapter 10

Fertilization takes

5 hours

implantation takes

6-10 days

week 6-9

start of development of internal organs

first 54 days, most susceptible to

teratogens

Why do nurses need to have a basic understanding of fetal development and conception?

to help patient make informed decisions about what they will do with their life

Fetal Development

• Zygotic stage

• Blastocyst stage

• Embryonic stage

• Fetal stage (longest stage)

• Fetal circulation

Genetics (focus of chromosomal abnormalities)

normal count: 46/23 pairs

x - female

y - male but can give x

Nurse role

assist with genetic counseling

Fetal development is measured in

trimesters and weeks

Zygotic stage

• conception

• outer 1/3rd of fallopian tube

• fusing of ovum and sperm

• combines maternal and paternal chromosomes (23 from each)

• establishes unique physical characteristics and determines sex

• who determines sex of baby → dad

• Zygote

blastocyst

• Hollow ball of cells

• Inner layer will form the embryo and the amnion

• Outer layer is the trophoblast which will eventually turn into the chorion and helps form the placenta

• Trophoblast attaches to endometrium

• progesterone maintains endometrium

• This is implantation (in upper portion of fundus due to vascular and muscle fibers to help clamp after birth) and considered a successful pregnancy

• Placental formation

• Inner cells become EMBRYO and the other cells surround and protect

• Ectoderm- CNS, special senses, skin, and glands

• Mesoderm- skeletal, urinary, circulatory, and reproductive organs

• Endoderm- respiratory system, liver, pancreas, and digestive system

Embryonic stage

• Begins at day 15 after conception & Continues through week 8

• All major body organs and external features in their BASIC form are completed during this time

• Embryonic membranes form

• Amnion inner layer + Chorion outer layer= Amniotic Sac

• At term amniotic fluid is roughly 1L- HOW DO WE GET AMNIOTIC FLUID? (partially pulled from mother’s circulation + fetal urine)

• helps indicate fetal’s urinary ability

• oligohydramnios <500

• polyhydramnios >2000

• Placenta development starts at end of week 2 and is complete by week 12

• Umbilical cord forms from the Amnion

• CONSIDERED THE LIFELINE

• 2 arteries supply to placenta

• vein goes back to mom for filtering

Placenta

hormone factory and transfer organ

• takes over mechanisms from baby’s lungs and liver

• protects from infection

• Blood pressure measures perfusion

Fetal stage

• End of week 8 and continues through birth

• All major systems at their basic form are present

• Refinement occurs throughout this stage

• Mature enough to be called a FETUS

Sex of baby can be determined at

around 20 weeks

fetal circulation

• Fetus has unique physiological needs

• doesn’t oxygenate or filter itself

• Vessels and shunts

• Direct oxygen rich venous blood to systemic circulation

• Ensures that O2 depleted venous blood bypasses lungs

• Lung function and liver function of baby are taken over by placenta

1. Ductus venosus- bypasses liver and connects the umbilical vein to the inferior vena cava

• has nutrients and oxygen

2. Foramen ovale- bypasses the right ventricle and lungs via an anatomic opening between right and left atrium; shunts blood

3. Ductus arteriosus- bypasses the lungs and connects the main pulmonary artery to the descending aorta

• has waste and unneeded things

Understand picture on slide 10

1 - ductus venosus closes with cord and closed by end of week 1

2 - foramen ovale: functional closure 1-2 hr after birth and initiated by 1st breath

3 - Ductus arteriosus: closes partly after 1st few breaths; secondary to increasing O2 levels (baby in hypoxic state); functional closure after 72hrs of birth

Genetics

• Study of heredity and its variations

• Birth defects occur in about 3% of all infants born in US

• Not crystal ball for telling the future but can help with preventing disabilities

• WHAT DOES THIS MEAN? (avoid procreating with someone with “bad genes”

• helps make informed decisions

• Traditionally genetics is used to help make decisions for child bearing or to prepare how to care for a child with a genetic disorder

• Tests & Screens

• Nuchal translucency - can indicate down syndrome; fluid filled space behind baby’s necks; 8-12 weeks

• Triple screens - blood tests on mom: AFP (by baby’s liver) ACG (hormone of pregnancy); checks on baby’s brain;

• Amniocentesis - 15-20 weeks; very invasive and high risk of infection and miscarriage; takes amniotic fluid and tests for genetic disorder

• Page 345

Genome project

• Gene therapy used to replace or repair defective or missing genes with NORMAL ones

• Genome= entire hereditary information encoded in the DNA

• Goal is to find strategies for prevention, diagnosis, and treatment of genetic diseases and disorders

• WHAT PROBLEMS CAN ARISE????

• “playing God”

• legal issues

• social issues

Inheritance and chromosomal abnormalities

• DNA is the hereditary material found in humans

• Genes are individual units of hereditary

• Mutations

• Karyotype - makeup of chromosomes; what DNA looks like

• Phenotype - physical appearance

• Chromosomal abnormalities occur due to the random events during early fetal development

• Abnormalities of chromosome number or structure → trisomies (genetic disorders)

• Congenital anomalies and intellectual disabilities

• Sex chromosome abnormalities

• Gender specific

• Affect sexual development, cause infertility, growth abn, possible behavioral and learning problems

Early miscarriages are from

chromosomal abnormalities

Late miscarriages

other conditions

• gynecological conditions

• others

Trisomies

• 21 - down syndrome

• 18 - edwards

• 13 - patau syndrome

Nurses role

• Nurses usually first person patient sees for preconception or prenatal information

• Educate and inform

• Gather patient and family information

• Help schedule testing

• Genetic disorders are life changing and can be life threatening

• Confidentiality

• Unbiased