In human beings, at the end of 12 weeks (first trimester) of...

1. In human beings, after one month of pregnancy, the embryo’s heart is formed. The first sign of a growing foetus may be noticed by listening to the heart sound carefully through the stethoscope, placed on the abdomen of the mother.
2. By the end of the second month of pregnancy, the foetus develops limbs and digits.
3. By the end of 12 weeks {first trimester}, most of the major organ systems are formed, and the limbs and external genital organs are well-developed.
4. The first movement of the foetus and the appearance of hair on the head is usually observed during the 5^th month.
5. By the end of 24 weeks (second trimester), the body is covered with fine hair, eyelids separate, and eyelashes are formed.