Comparing the writing of a book to the development of an embryo or foetus implies a period of inactive waiting, hanging around while the foetus grows on its own accord, without any conscious input. Nothing is further from the truth when it comes to writing.
I would prefer to imagine it this way:
In the depths of the creative psyche, something is conceived (perceived/apprehended/grasped). After this initial spark, a lot of input and unseen growing takes place as the idea develops and after a long period of nourishing (gestation/incubation) an idea is born, leaving its first few bloody footprints on the page. Now only does the hard work of nurturing the idea begin, the feeding and heeding, the pulling and pushing and slapping into shape, the gentle persuasion and the love, that will hopefully see it graduating from vague words to magnificent manuscript.
Some books die post-conception. Others are still-born and quickly buried. A few make it to maturity. A writer parent acknowledges them all as offspring, but it is the living ones she loves.