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Course: Maternity Nursing�Topic: Fetal Development and Circulation Part I

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Module Goals

The learner will be able to:

Differentiate between pre-embryonic and embryonic development
Explain key differences between monozygotic twins and dizygotic twins
List stages of fetal development with key landmarks and critical time frames

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Growth and Development:

Growth: Increase in the number and size of cells
Hyperplasia: Increase in cell number
Early in pregnancy, growth → hyperplasia
Hypertrophy: Increase in cell size
Late in pregnancy, growth → hypertrophy
Growth Pattern Development:
Cephalocaudal:From head to toe
Proximodistal: From center of the body outward

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Prenatal Development

A period that includes the 3 phases of fetal development:

The Germinal Period (Pre-Embryonic): Conception to implantation (approx. 14 days)
The Embryonic Period: From implantation- 3^rd week to 8^th week
The Fetal Period: From week 9 to the birth

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Pre-Embryonic/ Germinal Development:

Pre- Embryonic Development:

Conception to implantation
Lasts about 14 days
Zygote forms
Blastocyst forms, differentiation
Ends with Implantation

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Twins (Type and Formation)

Monozygotic or Identical Twins: Fertilized egg splits into 2 in first two weeks, they are genetically identical (Same genotype and Phenotype), 1/3 of twins are monozygotic
Dizygotic or Fraternal Twins: two separate eggs are released and fuse with 2 sperm cells. They possess different genotype and phenotype; Fertility drugs likely cause dizygotic twins

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Monozygotic Twins Vs. Dizygotic Twins

Monozygotic

Single fertilized ovum
Blastocyst: inner cell mass splits in two
Same sex and genotype
Same or different amniotic sac
Time of separation determines placenta/chorion/amnion separation

Dizygotic

Two separate ova, two sperms
Two separate genotypes
Different sex and different phenotype
2 separate amniotic sacs, placentas, and supporting structures

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Embryonic Development

From 3^rd to 8^th week
Embryo is formed
The placenta begins forming
Organogenesis
Morphogenesis
Cephalocaudal Development
Proximodistal Development
Crucial phase: Risk of Teratogenesis

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The Embryonic Development: This phase begins with the implantation of the blastocyst into the uterine wall (3^rd week to 8 weeks). After successful implantation, the blastocysts are termed as the embryo. The placenta starts forming, cells continue to differentiate.

Organogenesis occurs: Three germ layers of the embryo (ectoderm, mesoderm, and endoderm) develop into the internal organs. Growth now occurs in two major directions a) cephalocaudal (referring to structures from head to tail) The head develops at first 4 weeks and later the heart begins to beat at 8 weeks and, b) proximodistal development, referring to growth from the midline outward (arms develop at first and fingers develops later).

Morphogenesis occurs in this same stage: A biological process that causes the tissue, cells to form a definite shape. In the case of human development, at the embryonic stage, gills and tails are apparent but by the end of this stage disappear as the embryo takes on human-like shape and appearance.

During organogenesis and morphogenesis exposure to drugs ( including alcohol consumption and tobacco smoke) and chemicals and radiation,may cause congenital malformation (teratogenesis) resulting in malformations and miscarriaage of the fetus.

By the end of eight weeks, the embryo measures 1 inch and weighs 8 grams, it moves and responds to touch.

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Teratogens Cause Teratogenesis

Teratogens: Substances that can cause physical or functional defects in human embryo or fetus (exposure during the first 8 weeks of gestation).

Types of Teratogens:

Physical: Radiation, hyperthermia
Metabolic: Malnutrition, diabetes, thyroid disorders
Infection: Rubella, Herpes, Syphilis
Drugs and chemicals: Alcohol, Cocaine, Vitamin A

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Physical: Temperature more than 102ͦ F , Ultrasounds, X-rays, and electromagnetic Radiation can act like hyperthermic agents and may cause microcephaly, enlarged hearts, skeletal deformities, and miscarriages.

Metabolic: Diabetes mellitus, thyroid disorders, and malnutrition may affects the growth and development of the fetus. If a mother has thyroid problems, there is a higher risk of skeletal malformation, miscarriage, or placenta abruption. Similarly, a mother with DM is at risk for having an infant who is abnormally large

(macrosomic) or at risk for birth defects.

Infection: Certain infections like Rubella, Herpes, Syphilis, cytomegalovirus may cause malformations. For women who were infected with rubella in their first trimester, are at risk for delivering an infant with cataracts.

Drugs and chemicals: Drugs and chemicals ingested may cause teratogenic effect in the developing fetus. Alcohol, smoking, cocaine, Vitamin A, insecticides, pesticides, have been found to cause death, malformation, growth retardation, and functional defects. Alcohol consumption causes Fetal alcohol syndrome leading to cognitive disorders and facial abnormalities ( Fetal Alcohol Syndrome), Large amounts of vitamin A may cause cleft palate or malformed limbs.

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What Would the Nurse Do?

During a prenatal teaching class, a young mother says that almost everyone in her office smokes and she doesn't know how much it is going to affect her baby.

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Fetal Development in Weeks of Gestation:

From 9^th to 40^th week

At week 9, the embryo is referred to as fetus
Fetus matures to viability
Major structures start to develop
Refinement of organ structure and perfection of function continue

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Highlights of Fetal Development (Week 3 to week 40)

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9 Weeks Gestation

Fetus and placenta are visible
Fetal organs are in place
Heart has 4 chambers
Nose, other organs, nerves start developing
Tail goes away
Legs and body lengthen

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Development at 3 Months Gestation

Cartilage begins to develop into bone
Fetus can make a fist
Reflexes becomes more defined
Sex organs begin to differentiate
Baby has more human structure

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What Would the Nurse Do?

A newly pregnant woman comes to the maternal clinic and says that she is having occasional headaches ranging from mild to severe. She asks you if she could buy some painkillers from the local pharmacy and take it for a severe headache.

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Development at 4 Months

Fingers and toes develop
Hair, nails, teeth appear
The excretory and digestive systems continue to develop
Nervous system begins to develop
Can wiggle toes and fingers
Can make facial expressions

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Development at 5 Months

“Punches and kicks” can be felt by the mother
Sex organs are fully developed
Sucking reflexes (sucking, swallowing, hiccup) are developed
Cycle of sleep and wakefulness are present
Can hear sounds (mom’s voice)
Tiny teeth are formed under the gums
Vernix starts to develop
Lanugo develops

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What Would the Nurse Do?

A woman who is five months pregnant with her first baby, comes to the maternal clinic saying she was 20 weeks yesterday and has not been able to feel the kick. Her cousin, who is having her second baby, is also 20 weeks, and has felt her baby kick. She is worried if anything has happened to baby.

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Development at 6 Months

Fetus reaches viability
Rudimentary neurons develop in the brain
Fetus can feel pain
Eyelashes, eyebrows, and hair are fully-formed
Fat develops under the skin
Lungs develop

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Development at 7 Months

Brain develops more rapidly
Movements are more pronounced
Can open and close eyes and follow light

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Development at 8 Months

Lanugo disappears
Lungs are fully developed
Brain continues to develop rapidly
Body develops fat reserve
Bones fully developed

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Development at 9 Months

Fetus positions for birth
Muscles fully developed
Internal organs system fully developed
Fetal growth continues until 40 weeks
Birth happens (Full Term)

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What Would the Nurse Do?

During a community visit, a pregnant woman says her neighbors in the community say pregnancy lasts for 10 months whereas she read somewhere that it last for 9 months. She asks about how her baby breaths when it is inside her womb.

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Cultural Considerations

An Asian woman is usually shy and modest and would prefer to have prenatal teaching from a male healthcare provider
A Muslim woman would not allow her prenatal check-up with male care provider
Hispanic and Asian women consider pregnancy to be a normal phenomenon and might not seek prenatal care unless they feel unwell
In some cultures, women may neglect to go to the hospital, because they believe that doctors and nurses do not understand their beliefs and culture

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Glossary

Fertilization: The union of the egg and sperm
Conception: Fertilization
Implantation: Attachment of fertilized egg to the uterine wall
Viability: Ability to live and survive successfully outside of the womb
Vernix: A white cheesy substance that covers the body of fetus in order to protect the skin from amniotic fluid
Lanugo: soft and fine hair that develops in the body and limbs of fetus
Gestation: Pregnancy

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References:

Assegid. M. Obstetric and Gynecological Nursing. Ethiopia. Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education. 2003. pp. 36-46

Lally. M., Valentine-French. S. (2019). Lifespan Development: A Psychological Perspective. Retrieved on 8^th of September 2020 from http://dept.clcillinois.edu/psy/LifespanDevelopment.pdf

Tantibanchachai, C. (2014). The Embryo Project Encyclopedia: Teratogens. Retrieved on 7^th of September 2020 from https://embryo.asu.edu/pages/teratogens

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