I'm not entirely sure what you mean. I'd avoid using 'GCE' as a term as it is generally taken to mean A levels in the UK as GCE O levels were phased out here in the 1980s. O levels and IGCSEs are officially the same level of education. Each O level or IGCSE is a subject in its own right and there is nothing to stop you taking a mix of both.. You can complete each qualification but you cannot 'complete O levels' you just stop taking any more.