Postnatal means about the time after a baby is born. Hospitals talk about postnatal care: checks on the mother, checks on the baby, feeding help, and the first weeks at home. The word can look at the baby (postnatal growth) or at the mother (a postnatal clinic). British medical English likes postnatal a lot — people there often say postnatal depression; American English more often says postpartum depression for the same kind of illness. Though actually the two words sit very close, and doctors sometimes use them as if they were the same. Prenatal is the matching word for the time before birth. Postnatal is a clinic and textbook word; in kind everyday talk people often just say ‘after the baby was born.’