Perinatal means “at or around the time of birth.” Doctors use it for the stretch just before a baby is born, the birth itself, and the first days or weeks after. It is a hospital and textbook word. A parent at home would say “around the birth” or “when the baby was born,” not “in the perinatal period.” It is about that whole window, not only pregnancy and not only after the baby arrives. Though actually, hospitals do not all draw the line in exactly the same place — some count from a certain week of pregnancy to a week after birth; others go a little longer — so “around birth” is the right English idea, and the exact dates are a medical choice.