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Fetal Development

Fetal Development

Fetus at 12 weeks (source: www.nlm.nih.gov).

National Institutes of Health

When sperm is deposited in the vagina, it travels through the cervix and into the Fallopian tubes. Conception usually takes place in the Fallopian tube. A single sperm penetrates the mother’s egg cell, and the resulting cell is called a zygote.

The zygote contains all of the genetic information (DNA) necessary to become a child. Half of the genetic information comes from the mother’s egg, and half from the father’s sperm.

The zygote spends the next few days traveling down the Fallopian tube and divides to form a ball of cells. Further cell division creates an inner group of cells with an outer shell. This stage is called a “blastocyst”. The inner group of cells will become the embryo, while the outer group of cells will become the membranes that nourish and protect it.

The blastocyst reaches the uterus at roughly the fifth day, and implants into the uterine wall on about day six. At this point in the mother’s menstrual cycle, the endometrium (lining of the uterus) has grown and is ready to support a fetus. The blastocyst adheres tightly to the endometrium, where it receives nourishment via the mother’s bloodstream.

The cells of the embryo now multiply and begin to take on specific functions. This process is called differentiation, which produces the varied cell types that make up a human being (such as blood cells, kidney cells, and nerve cells).

There is rapid growth, and the baby’s main external features begin to take form. It is during this critical period of differentiation (most of the first trimester) that the growing baby is most susceptible to damage from:

  1. Alcohol, certain prescription and recreational drugs, and other substances that cause birth defects
  2. Infection (such as rubella or cytomegalovirus)
  3. Radiation from x-rays or radiation therapy
  4. Nutritional deficiencies

Specific Changes by Week



Week 3


Beginning development of the brain, spinal cord, and heart


Beginning development of the gastrointestinal tract



Weeks 4 to 5


Formation of tissue that develops into the vertebra and some other bones


Further development of the heart which now beats at a regular rhythm


Movement of rudimentary blood through the main vessels


Beginning of the structures of the eye and ears


The brain develops into five areas and some cranial nerves are visible


Arm and leg buds are visible



Week 6


Beginning of formation of the lungs


Further development of the brain


Arms and legs have lengthened with foot and hand areas distinguishable


Hands and feet have digits, but may still be webbed



Week 7


Nipples and hair follicles form


Elbows and toes visible


All essential organs have at least begun to form



Week 8


Rotation of intestines


Facial features continue to develop


The eyelids are more developed


The external features of the ear begin to take their final shape



The end of the eighth week marks the end of the “embryonic period” and the beginning of the “fetal period”.



Weeks 9 to 12


The fetus reaches a length of 3.2 inches


The head comprises nearly half of the fetus’ size


The face is well formed


Eyelids close and will not reopen until about the 28th week


Tooth buds appear for the baby teeth


Limbs are long and thin


The fetus can make a fist with its fingers


Genitals appear well differentiated


Red blood cells are produced in the liver



Weeks 13 to 16


The fetus reaches a length of about 6 inches


A fine hair develops on the head called lanugo


Fetal skin is almost transparent


More muscle tissue and bones have developed, and the bones become harder


The fetus makes active movements


Sucking motions are made with the mouth


Meconium is made in the intestinal tract


The liver and pancreas produce their appropriate fluid secretions



Week 20


The fetus reaches a length of 8 inches


Lanugo hair covers entire body


Eyebrows and lashes appear


Nails appear on fingers and toes


The fetus is more active with increased muscle development


“Quickening” usually occurs (the mother can feel the fetus moving)


Fetal heartbeat can be heard with a stethoscope



Week 24


The fetus reaches a length of 11.2 inches



The fetus weighs about 1 lb. 10 oz.


Eyebrows and eyelashes are well formed


All the eye components are developed


The fetus has a hand and startle reflex


Footprints and fingerprints forming


Alveoli (air sacs) forming in lungs



Weeks 25 to 28


The fetus reaches a length of 15 inches


The fetus weighs about 2 lbs. 11 oz.


Rapid brain development


Nervous system developed enough to control some body functions


Eyelids open and close


Respiratory system, while immature, has developed to the point where gas exchange is possible


A baby born at this time may survive, but the possibilities for complications and death remain high



Weeks 29 to 32


The fetus reaches a length of about 15-17 inches


The fetus weighs about 4 lbs. 6 oz.


Rapid increase in the amount of body fat


Rhythmic breathing movements occur, but lungs are not fully mature


Bones are fully developed, but still soft and pliable


Fetus begins storing iron, calcium, and phosphorus



Week 36


The fetus reaches a length of about 16-19 inches


The fetus weighs about 5 lbs. 12 oz. to 6 lbs. 12 oz.


Lanugo begins to disappear


Increase in body fat


Fingernails reach the end of the fingertips


A baby born at 36 weeks has a high chance of survival, but may require some medical interventions



Weeks 37 to 40


Considered full-term at 37 weeks


May be 19 to 21 inches in length


Lanugo is gone except for on the upper arms and shoulders


Fingernails extend beyond fingertips


Small breast buds are present on both sexes


Head hair is now coarse and thicker


Want to learn more about fetal development in preparation for exams? Discuss it with other experienced and prospective nurses.



      

      

      
+6
  • Nurse_gail_2009_max50

    gailp

    almost 7 years ago

    28 comments

    Sounds like an educator wrote this for a class!! I feel it definitely would be useful for student nurses for study purposes. Nice, concise and to the point.

  • Lulu2_max50

    Lulu7

    almost 7 years ago

    22 comments

    Very good article. The layout is clear and easy to understand. Excellent resource for expecting parents.

  • Fireworks_max50

    workingAngel

    about 7 years ago

    2 comments

    Good overview for expectant parents and will be helpful for students.

  • Nurse_cartoon_max50

    PittNurse

    about 7 years ago

    124 comments

    Great resource for expectant mothers and nurses going into OBGYN.

  • Photo_user_blank_big

    Account Removed

    about 7 years ago

    Good concise explanation. could be used even for the general population

  • Img_0817_max50

    Marieke

    about 7 years ago

    66 comments

    Good article, well laid out.. could've used this last year when I did my OB/Paeds rotation.. our workbook was badly put together!

  • 1024963740_m_max50

    vickielee1970

    about 7 years ago

    806 comments

    Very good, this article covers much of what I have just been studing in Maternity & Pediatric Nursing class

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