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    Fetal Development

    The growth of your baby is a continuous process that often conveys a sense of awe. The following information will help you understand your baby's rapid growth and highlights milestones in development. (Sizes and weights are approximate).

    First Trimester

    At the end of 4 weeks:

    • Embryo is 1/4 inch in length

    • Heart, digestive system, backbone and spinal cord begin to form

    • Placenta (sometimes called "afterbirth") begins developing

    • The single fertilized egg is now 10,000 times larger than size at conception
    At the end of 8 weeks:
    • Embryo is 1-1/8 inches in length

    • Eyes, nose, lips, tongue, ears and teeth are forming

    • Penis begins to appear in boys

    • Embryo is moving, although the mother cannot yet feel movement

    • Heart is functioning
    At the end of 12 weeks:
    • Fetus is 2-1/2 to 3 inches long

    • Weighs about 1/2 to 1 ounce

    • Nails start to develop and earlobes are formed

    • Fetus develops recognizable form

    • Arms, hands, fingers, legs, feet and toes are fully formed

    • Eyes are almost fully developed

    • By this stage, a fetus has developed most of his/her organs and tissues

    • Fetal heart rate can be heard at 10 weeks with a special instrument called a Doppler

    Second Trimester

    At the end of 4 months:

    • Fetus is 6-1/2 to 7 inches long

    • Weighs about 6 to 7 ounces

    • Fetus is developing reflexes such as sucking and swallowing. Fetus may begin sucking his/her thumb

    • Tooth buds are developing

    • Sweat glands are forming on palms and soles

    • Fingers are well defined

    • Sex is identifiable

    • Skin is bright pink, transparent and covered with soft, downy hair

    • Although recognizably human in appearance, the baby would not be able to survive outside the mother's body
    At the end of 5 months:
    • Fetus is 8 to 10 inches long

    • Weighs about 1 pound

    • Hair begins to grow on his/her head

    • Soft, woolly hair called lanugo will cover baby's body (and some may remain until a week after birth when it is shed)

    • Mother begins to feel fetal movement

    • Internal organs are maturing

    • Eyebrows, eyelids and eyelashes appear
    At the end of 6 months:
    • Fetus is 11 to 14 inches long

    • Weighs about 1-3/4 to 2 pounds

    • Eyelids begin to part and eyes open occasionally for short periods of time

    • Skin is covered with protective coating called vernix

    • Fetus is able to hiccup

    Third Trimester

    At the end of 7 months:

    • Fetus is 14 to 16 inches long

    • Weighs about 2-1/2 to 3-1/2 pounds

    • Taste buds have developed

    • Fat layers are forming

    • Organs are maturing

    • Skin is still wrinkled and red

    • If born at this time, he/she will be considered a premature baby and require special care
    At the end of 8 months:
    • Fetus is 16-1/2 to 18 inches long

    • Weighs about 4 to 6 pounds

    • Overall growth is rapid this month

    • Tremendous brain growth occurs at this time

    • Most body organs are now developed with the exception of the lungs

    • Movements or "kicks" are strong enough to be visible from the outside

    • Kidneys are mature

    • Skin is less wrinkled

    • Fingernails now extend beyond fingertips
    At the end of 9 months:
    • Fetus is 19 to 20 inches long

    • Weighs about 7 to 7 1/2 pounds

    • Skin is pink and smooth

    • The lungs are mature

    • Baby is now fully developed and can survive outside mother's body

    • He/She settles down lower in the abdomen in preparation for birth and may seem less active
    For further information, review the video The Miracle of Life and the book A Child is Born by Lennart Nielson for a pictorial review of your baby's development. Both are available at Newborn Connections.