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8.4: Fetal Stage

  • Page ID
    228501
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    Learning Objectives
    1. Define the fetal period.
    2. Identify the beginning and end of the fetal period in prenatal development.
    3. Describe the significant physical developments that occur during the fetal period, including organ system maturation.

    The Fetal Period

    From the ninth week until birth, the organism is referred to as a fetus. During this stage, the major structures are continuing to develop. By the third month, the fetus has all its body parts, including external genitalia. The fetus is about 3 inches long and weighs about 28 grams. In the following weeks, the fetus will develop hair, nails, teeth, and the excretory and digestive systems will continue to develop.

    clipboard_e2fd2aee502138c4df60bd87334d94b07.png
    Figure \(\PageIndex{1}\): A human fetus. Image by lunar caustic is licensed under CC BY-SA 2.0

    During the 4th to 6th months, the eyes become more sensitive to light, and hearing develops. The respiratory system continues to develop, and reflexes such as sucking, swallowing and hiccupping, develop during the 5th month. Cycles of sleep and wakefulness are also present at this time. The first chance of survival outside the womb, known as the age of viability, is reached at about 24 weeks (Morgan, Goldenberg, & Schulkin, 2008). Many practitioners hesitate to resuscitate before 24 weeks. The majority of neurons in the brain have developed by 24 weeks, although they are still rudimentary, and the glial cells or nurse cells, which support neurons, continue to grow. At 24 weeks, the fetus can feel pain (Royal College of Obstetricians and Gynecologists, 1997).

    Between the 7th and 9th months, the fetus is primarily preparing for birth. It is exercising its muscles, and its lungs begin to expand and contract. The fetus gains approximately 5 pounds and 7 inches during the last trimester of pregnancy, and by the 8th month, a layer of fat develops under the skin. This layer of fat serves as insulation, helping the baby regulate its body temperature after birth.

    At around 36 weeks, the fetus is almost ready for birth. It weighs approximately 6 pounds and measures about 18.5 inches in length. By week 37, all of the fetus’s organ systems are developed enough that it could survive outside the mother’s uterus without many of the risks associated with premature birth. The fetus continues to gain weight and grow in length until approximately 40 weeks. By then, the fetus has very little room to move around, and birth becomes imminent. The progression through the stages is shown in the following figure. 26

    clipboard_e84e4c9aadcc7ab6ebc65331c166ea76e.png
    Figure \(\PageIndex{2}\): The development of a fetus. Image by CNX Psychology is licensed under CC BY 4.0

    References, Contributors and Attributions

    26. Lifespan Development: A Psychological Perspective (pages 44-45) by Martha Lally and Suzanne Valentine-French is licensed under CC BY-NC-SA 3.0


    This page titled 8.4: Fetal Stage is shared under a CC BY-NC license and was authored, remixed, and/or curated by Heather Carter.