If someone were to suppose to give birth on june 9th but gave birth early on may 18th, around what time would they have to get pregnant?

Need much more info: Unfortunately,neither the actual date of the birth nor the "estimated due date" is a reliable or useful information to determine gestational age or estimate the time of conception. Early pregnancy sonograms, the baby's birth weight, the pediatrician assessment of the baby's age by a set of physical/neuromotor criteria at birth...are some ways to help you get an approximate answer to your question.