conception fetal development & genetics chapter 10 mary l. dunlap msn, fall 2015

CONCEPTIONFETAL 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 ofFetal 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

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

• 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

• Cystic fibrosis

• Phenylketonuria

• Sickle cell

• Tay-Sacks

Structural Abnormalities

• 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

• Alpha-fetoprotien

• Diagnostic Amniocentesis

• Chorionic Villus Sampling CVS

• Percutaneous umbilical blood sampling PUBS

• Fetal nuchal translucency

• Types of Ultrasounds 7 min

• Quad screen