The period of gestation when the rudiments of all major organ systems are established in the first trimester.
- In humans, pregnancy lasts for around 9 months.
- After one month of pregnancy, the human heart is developed.
- By the end of the first trimester which is the initial 12 weeks, most of the major organ systems are formed including the limbs and the external genital organs.
- During the fifth month, the first movement of the fetus is observed and hair appears on the head of the fetus.
- By the end of the second trimester i.e., after 24 weeks, the body gets covered with very fine hair, eyelids get separated and eyelashes are formed.
- By the end of the third trimester i.e., at the end of 9 months, the fetus is fully developed.
Thus, the period of gestation when the rudiments of all major organ systems are established in the first trimester.
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