Answer:
The first and Shortest stage of prenatal development is Germinal stage, where the zygote begins to grow in complexity during first two weeks of conception.
The embryonic stage lasts from 2-8 weeks following fertilisation,when major organ and basic anatomy begin to develop.
The fetal stage lasts from 8 weeks until birth and involved the differentiation of major organs.
Explanation:
Periods of pregnacy and major events are as follows:
- Implantation follows the germinal stage.
- Embryonic stage begins at 2 weeks and following events occur:
- End of one month : Embryo's heart begins to beat.
- End of second month: limbs become paddle like.
- Fetal stage begins:
- first trimesters: major organ systems established.
- End of fourth month: nerve fibre formation begins.
- End of fifth month: First movement of foetus,; eruption of hair.
- End of sixth month: Fine hairs appear on body, eyelids separate.
- End of eighth month: Testes descends into scrotum.
- End of ninth month: Foetus completely developed and ready for birth