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    Twins Development 1st Trimester Highlights

    A lot has happened in the past three months. Your twins are only 3 or 4 inches long, but already can open and close their fists and mouths. Fingernails and toenails are just beginning to develop. Already, your tiny babies have:

    • Brains, spinal cords, and flexible backbones.
    • Lungs, but not fully developed.
    • Hearts beating 120 to 160 beats per minute.
    • All major organs, but not fully developed.
    • Soft skeletons.
    • Eyes with eyelids that stay closed.
    • Noses, mouths, and chins.
    • Distinct fingers and toes and tiny fingernails.
    • Genitalia, but not fully developed.
    • Little teeth buds.

    WebMD Medical Reference

    Reviewed by Nivin Todd, MD on July 25, 2014

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