In a human female's pregnancy. - By the end of 12 weeks ( 1‌st ‌ trimester), most of major organ systems are formed (not by end of 8 weeks). - After one month of pregnancy, the embryo's heart is formed. - By the end of second month of pregnancy, the foetus develops limbs and digits. - The first movements of foetus and appearance of hair on head are usually observed during the fifth month.