You can if you want. Or don't. Forms have not a damned thing to do with it.
My mother had a baby between my older sister and older brother. She was in her eighth month, and fell down a flight of ice-covered stairs. The fall sent her into premature labor, and the baby lived in the hospital for about a week before he died. In all the almost-60 years since then, I can't recall her ever having to fill out a form that asked her the total number of babies she'd had; the only questions she was ever asked on forms was along the lines of, "How many children do you have living in your home?"
By the way, she only "knew" my brother for eight months. She's mourned him for 60 years.