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Fact Sheet - Prenatal Development

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  • The heart of the developing human beats approximately 54 million times before birth.
  • Pregnancy in humans normally lasts approximately 38 weeks as measured from the time of fertilization, or conception, until birth.
  • Biologically speaking, "human development begins at fertilization," with the union of the male and female reproductive cells.
 Full Text [Fact #6051]
  • The heart begins beating 3 weeks and one day following fertilization.
  • Between 3 and 4 weeks, the body plan emerges as the brain, spinal cord, and heart of the embryo are easily identified alongside the yolk sac.
  • The embryo begins to make spontaneous and reflexive movements 5 1/2 to 6 weeks after fertilization. Prenatal movement is necessary to promote normal bone and neuromuscular development.
 Full Text [Fact #6088]
  • Electrical activity of the embryo's heart recorded at 7 1/2 weeks reveals a wave pattern similar to the adult's.
  • By 7 1/2 weeks fingers are separate and toes are joined only at the bases.
  • During the embryonic period, the human embryo grows from a single cell into the nearly one billion cells which form over 4,000 distinct anatomic structures.
  • The 8-week embryo possesses more than 90% of the structures found in adults.
 Full Text [Fact #6114] Full Text [Fact #6114]
  • The 9-week fetus can grasp an object, move the head forward and back, open and close the jaw, move the tongue, sigh, and stretch.
  • By 9 weeks after fertilization, nerve receptors in the face, the palms of the hands, and the soles of the feet can sense light touch.
  • Between 9 and 10 weeks body weight increases by over 75%.
  • Bone formation is underway in most bones by 10 weeks.
  • Fat deposits begin to fill out the cheeks by 14 weeks.
 Full Text [Fact #6148]
  • By 20 weeks the cochlea, which is the organ of hearing, has reached adult size within the fully developed inner ear. From now on, the fetus will respond to a growing range of sounds.


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