My Mother in law recommended me to read the Bhagavad Gita during pregnancy. I did it but why do you think it helps?

Read any book, it's good for you. You will have an ample amount of time during pregnancy. People rate books higher than TVs :). It's your time, spend it wisely. As far as Bhagavad Gita is concerned it's a very good source of filtered wisdom. It will definitely help you whether it will help your kid or not is another question. If you feel happy the kid inside you will feel happy. It's a part of you and will experience some extent of you emotions be it happiness or sadness. Try to be healthy, happy and cheerful. As the Gita says: Karmanye Vadhikaraste, Ma phaleshou kada chana – You have the right to perform your actions, but you are not entitled to the fruits of the actions. Ma Karma Phala Hetur Bhurmatey Sangostva Akarmani – Do not let the fruit be the purpose of your actions, and therefore you won’t be attached to not doing your duty.