Having 'week of gestation' and/or a bespoke question field, as an option on registration form

There is currently nowhere on the registration form for parents to record the week of gestation the child was born, and any complications at birth. Our nursery is doing the ‘Prem award’ and one of the conditions is that we ask for this written information at registration. Maybe a bespoke box that nurseries can add their own unique question on the reg form, with a field for typing in an answer for the parents? As there is no options for a bespoke question on the reg form at the moment.