Final answer:
The question seems to be incorrectly asking about changes in the father by the end of the third month. Instead, fetal development progresses significantly by the end of the third month with the formation of major organs, growth of lanugo, and activity. By the end of the third trimester, the fetus is almost ready for birth, showing considerable growth in size and weight.
Step-by-step explanation:
The question appears to ask about changes in the father by the end of the third month, which may be a reference to the phenomenon commonly known as 'couvade syndrome' or 'sympathetic pregnancy' where a partner experiences some pregnancy-like symptoms. However, the provided context and additional information are all focused on fetal development, not changes in the father. Therefore, I am assuming there is a misinterpretation in the question, and it actually refers to the changes occurring in the fetus by the end of the third month.
By the end of the third month of pregnancy, the fetus has undergone significant development. This is part of the first trimester, and notable changes have occurred. By the end of this period, all major organs and systems have begun to form. Fetal developments that occur between weeks 9 and 12 include the differentiation of the reproductive organs and the beginning functioning of the thyroid, liver, pancreas, and kidneys. The fetus becomes more active, although movements remain mostly uncontrolled. Fine hair called lanugo begins to grow on the face and will eventually cover the body.
Towards the end of the third trimester, the fetus experiences rapid growth, particularly in body size and weight due to an increase in body fat. Major organs have matured, and the fetus is preparing for birth.