The chord symbol iii could be followed by the letter a to indicate that it is F# minor chord in root position (ie not inverted) - D major scale chord iiia. Instead, iii could be followed by the letter b to indicate that it is F# minor chord in 1st inversion - D major scale chord iiib.
According to the Centers for Disease Control and Prevention, a baby is considered an infant until he reaches one year of age. During this stage, the infant reaches several developmental milestones.
Which is that of the stages of Human Development. So, in terms of human development an embryo is not a fetus, like a fetus is not a baby, like a baby is not a toddler, like a toddler is not a young adult... etc. Basically if you find the definition of Embryo it is: a developing human from conception to 8 weeks.