First trimester – conception to 12 weeks. Second trimester – 12 to 24 weeks. Third trimester – 24 to 40 weeks.
Explanation:
The process of prenatal development occurs in three main stages. The first two weeks after conception are known as the germinal stage, the third through the eighth week is known as the embryonic period, and the time from the ninth week until birth is known as the fetal period.
