Fact Sheet - Prenatal Development

• 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.

 

• 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.

 

• 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.

  

• 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.

 

• 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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