Fact Sheet - Prenatal Development

• Major circulatory system changes occur at birth allowing the fetus to survive the transition from the uterus to the outside world.

• The heart of the developing human beats approximately 54 million times before birth.

• By approximately 15 days after fertilization, the embryo's right and left sides are identifiable as is the location of the developing head.

 

• The amnion is a clear membrane within which the embryo and fetus develop until birth. It is first seen 7 to 8 days after fertilization.

• By 3 weeks the brain is dividing into three primary sections called the forebrain, midbrain, and hindbrain.

 

• The heart begins beating 3 weeks and one day following fertilization.

• The circulatory system is the first body system, or group of related organs, to achieve a functional state.

 

• Upper and lower limb development begins with the appearance of the limb buds by 4 weeks after fertilization.

 

• 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.

 

• By 9 weeks, thumb sucking begins and the fetus can swallow amniotic fluid.

 

• By 26 weeks the eyes produce tears.

• Tooth development begins approximately 13 weeks after fertilization.

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