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Month by month development of your unborn baby 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
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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
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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
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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
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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
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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
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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.
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