First, it is recommended that the father is the one who says Adhan in the right ear of the newborn baby. Scholars said: "The word of Tawhid (monotheism) will be the first thing to be heard by the baby." It is remarkable that according to the experiments performed on babies, the effects which the babies are exposed to in their early years have a great influence on them when they grow up. Also, some of these effects determine the type of their tests in the future.
There are many studies done in psychology and embryological psychology that you might not believe their results. It has been indicated in these results that the embryo owns a full psychological life. For instance, if it feels that its mother does not want to have it, it responds by making moves that cause pain to the mother's belly, and they have their unhealthy effects on her. This is a wide topic which I read about once, and I tackled it in one of the Friday sermons. The main thing that is left in my mind about this topic is that the embryo has a full psychological life.
The Prophet, may Allah have peace and blessing upon him, said Adhan in the right ear of the newborn baby. In some weak Ahadeeth it was reported that he said Iqamah in the left ear, but let us stick to the authenticated Prophetic action: