The word pregnancy refers to the condition of having a child growing in the female body. This is also called being pregnant.
Ex: Her pregnancy was difficult as the child grew and became more active. She could feel every kick as the developing baby moved in her womb.
You can also use the word infancy to talk about an idea or thought that is not fully developed. It is used in the phrase in its infancy to refer to an idea as young and incomplete.
Ex: The inventor could not draw a picture of the machine he imagined. The idea was still in its infancy.
Ex: The company is only one-year-old and has not yet made money. The owners are being patient because the business is still in its infancy.
The word birth describes the bodily process of having, or bearing, a child. It is also common to refer to it as childbirth. To give birth is a common phrase that means the same thing.
Ex: On the day of his birth, Jack's mother smiled knowing she would soon hold her baby boy.
The phrase give birth to is also used as a popular idiom. In this case, it means to originate, or create, something.
Ex: Her idea for a main character gave birth to a well written novel. It received excellent reviews from the critics.