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    Children's Health

    Pregnancy: Your First Trimester Changes

    The first trimester is a time of rapid development for your baby. Because your baby is growing so quickly, it is important that you start a healthy lifestyle right away. By the end of the first trimester, your baby has formed all of its major body organs and weighs just over an ounce.

    Month 1 (weeks 1 to 4)

    The placenta (the organ that nourishes your baby) begins to form. The brain, spinal cord, heart, gastrointestinal tract, and lungs begin to develop. Your baby is about ¼ inch long by the end of the first month.

    Side view of female body showing reproductive system and inset of 1 month embryo.
    Actual size of baby is 1/4".

    Month 2 (weeks 5 to 8)

    All of your baby’s major body organs form. The face, fingers, toes, ears, and eyes appear. By the end of the month, your baby is about 1 inch long.

    Side view of female body showing reproductive system and inset of 2 month embryo.
    Actual size of baby is 1".

    Month 3 (weeks 9 to 12)

    Your baby can open and close its fists and mouth. The sexual organs begin to form. As the first trimester ends, your baby is about 3 inches long.

    Side view of female body showing reproductive system and inset of 3 month embryo.
    Actual size of baby is 3".

    Online Medical Reviewer: Donna Freeborn PhD CNM FNP
    Online Medical Reviewer: Heather M Trevino BSN RNC
    Online Medical Reviewer: Irina Burd MD PhD
    Date Last Reviewed: 12/1/2022
    © 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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    Southern New Mexico
    Surgery Center

    2301 Indian Wells Rd. Suite B
    Alamogordo, NM 88310
    www.snmsc.org

    Phone: 575.437.0890
    Fax: 575.437.0905
    Email: info@snmsc.org

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