Early Stages of Development of a Human Fetus

(From “The Multi-Dimensional Human Embryo,” University of Michigan)

Some Early Events of Fetal Development:

1. Egg is fertilized

2. Cell divides, is called “blastocyst”

3. Blastocyst moves down fallopian tube to uterus

4. Blastocyst begins to implant in the wall of the uterus about 7 days after fertilization, which means a larger number of postovulatory days.

5. The implantation process is completed in the in the 2^nd week after fertilization

6. The implanted blastocyst is now an embryo. Some see this as the beginning of pregnancy, some claim that pregnancy begins with fertilization.

Critical Periods of Human Development

Light blue bars indicate periods when organs are most sensitive to damage from alcohol, viral infection, etc. (from Human Biology by Starr and McMillan). For more detailed information on fetal development, see the University of Pennsylvania website at http://www.med.upenn.edu/meded/public/berp/overview/BV_1.html

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