As an English learner it is difficult for a person to understand the terms like 'embryo' and 'fetus'... thus can we use the home-made term 'undeveloped child' for an embryo or fetus? Will that fit best?
Actually the thing that confuses me as a reader is that 'undeveloped child' may mean "a child who isn't grown up well" or "a child who's not taken well care of, as far as grooming and learning are concerned"... so if you say:
She lost an undeveloped child before giving him birth.
Will it let the reader or listener understand that the talk is about a baby lost during pregnancy?
And also, Can a fetus be called a baby?"