In my opinion, the site to use for Scottish births, deaths & marriages and all the censuses is Scotlandspeople.http://www.scotlandspeople.gov.uk/welcome.aspx
Statutory registration of births started in Scotland in 1855. In that first year the birth certs contained extra information eg how many children the parents already had, plus where and when they married. So if there was a child born that year, you should definitely look for that cert. Then, as I understand it, they dropped all the extra information for the years 1856 to 1859, but from 1860 onwards resumed recording where and when the parents married.