CONCEPTION
FETAL DEVELOPMENT &
GENETICS
Chapter 10
Mary L. Dunlap MSN,
Fall 2015
Fetal Development
• Measured in the number of weeks
after fertilization
• Average pregnancy lasts 280 days
or 40 weeks from the date of the
last menstrual period (LMP)
• Fertilization usually occurs 14 days
after the LMP
Three Stages of
Fetal Development
• Preembryonic stage: fertilization
through the second week
• Embryonic stage: end of second
week through the eighth week
• Fetal stage: ninth week until birth
Preembryonic Stage
(Stage 1)
• Fertilization - union of the ovum and
sperm in the outer 3rd of the fallopian
tube creating a zygote
• The union restores the diploid number of
46 chromosomes
Fetal Development
• Fertilization
Preembryonic Stage
(Stage 1)
• Zygote undergoes cleavages
(mitosis) as it is transported to the
uterine cavity in 72⁰
• Cleavages create a ball of 16 cells
called a morula, which divides into
cells that form fetal structures
Preembryonic Stage
(Stage 1)
• Blastocysts - inner cells form the
embryo and the amnion
• Trophoblasts - outer cells form the
embryonic membranes, Chorion and
placenta
• Implantation in the endometrium
occurs between the 7th to 10th day.
Embryonic Stage
(Stage 2)
Fetal membranes start forming
around the time of implantation
• Decidua- endometrial linning
• Chorion-placenta
• Embryonic germ layers- ectoderm,
mesoderm, endoderm
• Amnion- lines the amniotic sac &
forms the umbilical cord
Embryonic Stage
(Stage 2)
Amniotic Fluid
• Surrounds embryo,
• Helps maintain a constant body
temperature for the fetus
• Permits symmetric growth and
development
• Cushions the fetus from trauma
Embryonic Stage
(Stage 2)
Amniotic Fluid Function
• Allows the umbilical cord to be relatively
free of compression
• Promotes fetal movement to enhance
musculoskeletal development
Embryonic Stage
(Stage 2)
Umbilical cord
• Life line between mother and embryo
• 1 large vein & 2 small arteries (AVA)
• Wharton’s jelly surrounds the blood
vessels preventing compression
• Term length 22 in. / 1 in. wide
• Central insertion site on the placenta
Embryonic Stage
(Stage 2)
Placenta
• Functioning by end of the 3rd wk.
• Produces hormones that control the
basic physiology of the mother and near
term mature fetal organs for life outside
of the uterus
• Protects the fetus from immune attack
by the mother
• Removes waste produced by the fetus
Embryonic Stage
(Stage 2)
• Placental barrier prevents the mix of
maternal blood with fetal blood
Placental Hormones
• Human chorionic gonadotropin (hCG)
• Human placental lactogen (hPL)
• Estrogen, progesterone
• Relaxin
Embryonic Stage
• Maternal Fetal circulation via the
placenta
Development
• Embryonic and Fetal Development
• Table 10-1 p 286-287
Development
• Fetal Development
Development
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Embryonic stage 3rd to 8th wk.
Neural tube forms
Brain waves detectable
Heart development completed and beats
Arms and legs move
Resembles a human being
Weight 1gram
Fetal Stage
(Stage 3)
9Th week to Birth
• 12 wks.- heart beat heard with Doppler,
sex is distinguishable, placenta
formation completed
• 13-16 wks.- fetal movement (quickening)
felt by mother
• 17-20 wks.- heart beat can be heard
with a stethoscope
Fetal Stage
(Stage 3)
• 21-24 wks.- lungs produce surfactant
• 24-32 wks.- alveoli begin to mature,
eyelids can open and close, increase in
subcutaneous fat
• 32-40 wks.- fetus kicks actively, lanugo
decrease, weight 7-8 lb’s
Length 17.3-19.2 in
Fetal Circulation
• Needed to sustain the fetus
• Must develop quickly and accurately
since the fetal nutrient needs Increase
as the embryo advances to a fetus
• Oxygen received from the placenta
• Placenta functions for the fetal lungs
and liver
Fetal Circulation
Three unique shunts
• Ductus Venosus
• Foramen Ovale
• Ductus Arteriosus
• Fetal Circulation Prior to Birth
• Foramen Ovale & Ductus Arteriosus
Genetics
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Human Genome Project 1990
International 13 year study
Goal map the human genome
Better understanding how genetic
changes contribute to disease
• Helped develop new strategies for
prevention, diagnosing and treating
diseases and disorders
Genetics
• Genetic services are becoming an
integral part of medical care.
• Diagnostic procedures have provide the
opportunity to increase survival rates.
• Nursing needs basic knowledge to be
able to help their patients.
Genetic Disorders
• Result from abnormalities in patterns of
inheritance or chromosomal
abnormalities
Chromosomal Abnormalities
• 1 in 33 infants born in the U.S. have birth
defects and genetic disorders
• Numeric abnormalities
• Structural abnormalities
Numeric Abnormalities
• Often result due to failure of the
chromosome pair to separate
• Few of these abnormalities are
compatible with normal development
and end in spontaneous abortion
• Two common abnormalities
Monosomies and Trisomies
Numeric Abnormalities
• Monosomies-missing a chromosome
only one instead of a pair
• Trisomies - three of a particular
chromosome
• Trisomy 21(Down syndrome)
Structural Abnormalities
• Breakage and loss of a portion of one or
more chromosomes and the broken
ends rejoin incorrectly
• Altered structure can be a deletion,
duplication, inversion or translocation
• Mutation
Structural Abnormalities
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Cystic fibrosis
Phenylketonuria
Sickle cell
Tay-Sacks
Structural Abnormalities
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Huntington's disease
Polycystic kidney disease
Cri du Chat syndrome
Fragile X syndrome
Threats to Development
The following are capable of inducing
abnormal fetal structure or function by
interfering with normal fetal development
• Teratogens
• Medications
• TORCH infections
Genetic Evaluation and
Counseling
• Genetic counseling is an evaluation of
an individual to confirm, diagnose or rule
out a genetic condition.
Genetic Evaluation and
Counseling
• Ideal time: before conception
“ preconception counseling provides
the opportunity to identify, reduce,
and plan for potential risks.
Genetic Evaluation and
Counseling
• Reasons an individual should be
referred to genetic counseling (see Box
10-2 Pg.302)
Genetic Evaluation and
Counseling
• Genetic Testing
• Genetic Counseling
• Discussion about Genetic Counseling
Nurse’s Role
• Discussing costs, benefits, and risks of
using health insurance, and potential
risks of discrimination
• Recognizing ethical, legal, and social
issues
• Safeguarding privacy and confidentiality
• Monitoring emotional reactions after
receiving information
Nursing Role
• Providing emotional support
• Referring to appropriate support groups
• Beginning the preconception
counseling process and referring for
further genetic information
• Taking a family history (Box 10-4 Pg.
257)
Nursing Role
• Scheduling genetic testing
• Explaining the purposes, risks/benefits
of all screening and diagnostic tests
(see Laboratory and Diagnostic Tests
10-1 Pg. 258)
• Answering questions and addressing
concerns
Prenatal Testing and Hard
Choices
• http://www.youtube.com/watch?v=7rrA4F_
NY3w
Antepartum Testing
• Understanding Prenatal testing
Antepartum Testing
• Alpha-fetoprotein
• Amniocentesis
• Chorionic villus
sampling
• Percutaneous
umbilical blood
sampling
• Fetal nuchal
translucency
• Level II
ultrasound
• Triple marker
test
Antepartum Testing
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Alpha-fetoprotien
Diagnostic Amniocentesis
Chorionic Villus Sampling CVS
Percutaneous umbilical blood sampling
PUBS
• Fetal nuchal translucency
• Types of Ultrasounds 7 min
• Quad screen