What is the annual number of IT certifications obtained?

I’m trying to understand the overall size of the market for IT certifications. I have been looking for a source that provides data for the annual number of certifications received for the major IT certifications (Cisco, Microsoft, HP, CTIA, etc.), but have not found any one source.

If you have this data or can point me towards it, that would be really helpful.

Thanks,
Ripan