Fact Sheet
Prenatal Development Facts
- As the first blood cells appear in the yolk sac 3 weeks after fertilization, blood vessels form throughout the embryo, and the tubular heart emerges.1
- At approximately 3 weeks, the heart grows rapidly and begins folding in upon itself as separate chambers begin to develop.2
- The heart begins beating 3 weeks and one day following fertilization.3
- The circulatory system is the first body system, or group of related organs, to achieve a functional state.4
- Four weeks, 4 days after fertilization, the heart changes color as blood enters and leaves its chambers with each beat, as seen in The Biology of Prenatal Development DVD.
- Electrical activity of the embryo's heart recorded at 7 1/2 weeks reveals a wave pattern similar to the adult's.5
- The heart of the developing human beats approximately 54 million times before birth.
- Major circulatory system changes occur at birth allowing the fetus to survive the transition from the uterus to the outside world.7
Footnotes
1Carlson, 2004; O'Rahilly and Müller, 1987; Gilmour, 1941.
2Campbell, 2004; O'Rahilly and Müller, 1987; Navaratnam, 1991; Carlson, 2004.
3Campbell, 2004; Wisser and Dirschedl, 1994; O'Rahilly and Müller, 1987; Navaratnam, 1991; Kurjak and Kos, 1994; van Heeswijk et al., 1990; Gittenger-de Groot et al., 2000; Gilbert-Barness and Debich-Spicer, 1997; Gardner and O'Rahilly, 1976; de Vries and Saunders, 1962; Carlson, 2004.
4Moore and Persaud, 2003.
5Gardner and O'Rahilly, 1976; Straus et al., 1961.
6Prenatal Form and Function Appendix, 2005.
7Carlson, 2004.
Bibliography
Campbell S. 2004. Watch me grow: A unique 3-dimensional week-by-week look at your baby's behavior and development in the womb. New York: St. Martins.
Carlson BM. 2004. Human embryology & developmental biology. 3rd ed. Philadelphia: Mosby.
de Vries PA, Saunders JB. 1962. Development of the ventricles and spiral outflow tract in the human heart. Contributions to Embryology. Carnegie Institution of Washington. 37:87-114.
Gardner E, O'Rahilly R. 1976. The nerve supply and conducting system of the human heart at the end of the embryonic period proper. Journal of Anatomy. 121(3):571-587.
Gardner E, O'Rahilly R. 1976. The nerve supply and conducting system of the human heart at the end of the embryonic period proper. Journal of Anatomy. 121(3):571-587.
Gilbert-Barness E, Debich-Spicer D. 1997. Cardiovascular system. In: Gilbert-Barness, editor. Potter's Pathology of the Fetus and Infant. Vol 1. St. Louis: Mosby.
Gilmour JR. 1941. Normal haemopoiesis in intra-uterine and neonatal life. Journal of Pathology and Bacteriology. 52:25-55.
Gittenger-de Groot AC, Bartelings MM, Poelmann RE. 2000. Normal and abnormal cardiac development. In: Allan L, Hornberger LK, Sharland G, editors. Textbook of fetal cardiology. London: Greenwich Medical Media Limited. p. 15-27.
Kurjak A, Kos M. 1994. The fetus as a patient. Acta medica Croatica. 1994;48(3):95-8.
Moore KL, Persaud TVN. 2003. The developing human, clinically oriented embryology. 7th ed. Philadelphia: W.B. Saunders.
Navaratnam V. 1991. Organisation and reorganisation of blood vessels in embryonic development. Eye. 5(Pt 2):147-150.
Navaratnam V. 1991. Organisation and reorganisation of blood vessels in embryonic development. Eye. 5(Pt 2):147-150.
O'Rahilly R, Müller F. 1987. Developmental stages in human embryos. Washington: Carnegie Institution.
Prenatal Form and Function Appendix. 2005. Prenatal form and function � the making of an earth suit: Appendix. The Endowment for Human Development.
Straus R, Walker RH, Cohen M. 1961. Direct electrocardiographic recording of a twenty-three millimeter human embryo. American Journal of Cardiology. 8:443-447.
van Heeswijk M, Nijhuis JG, Hollanders HMG. 1990. Fetal heart rate in early pregnancy. Early Human Development. 22(3):151-156.
Wisser J, Dirschedl P. 1994. Embryonic heart rate in dated human embryos. Early Human Development. 37:107-115.
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