By Dan Primack
December 5, 2012

FORTUNE — A growing number of tech startups are having trouble graduating from seed or angel funding to traditional venture capital. And it’s only going to get worse.

This is the so-called Series A crunch, which might as well be called The Social Network effect — since the bottleneck all begins with a spike in the number of aspiring Zuckerbergs and those wealthy patrons who want in on the ground floor

Most of the commentary so far has been qualitative, including from yours truly. But I wanted to see some actual numbers, and reached out to the folks at CB Insights (who seem to have the industry’s best seed/angel data). I also asked them to only include U.S. tech startups, since there is much less seed and angel funding in the life sciences and energy sectors.

Take a look at some of what they sent over:

What you immediately notice is that the number of seed/angel deals has exploded, while the number of Series A deals has grown at a much slower pace. For example, there were virtually the exact same number of seed/angel deals in 2009 as there were Series A deals. So far this year, on the other hand, seed/angel deals are outpacing Series A deals by more than 2.5-to-1.

The ratio within a given year isn’t necessarily important on its own, since a company typically raises Series A funding 12-18 months after being seeded. But we see the gap continuing to grow.

Series A deals in 2011 represented just 91% of 2010 seed/angel deals, compared to 109% the prior period. That figure dropped to just 65% in 2012, and I would expect the plummet to continue into 2013. After all, the number of seed/angel deals continues to rise and VC fundraising difficulties may mean that Series A commitments have plateaued.

More: Stop with the Series A schadenfreude

To be sure, there are some questions that the data doesn’t answer. The most pressing is what percentage of the Series A deals are for companies that had been seeded, compared to those that were otherwise bootstrapped or got traditional VC from the get-go. I also don’t yet know what number of those seeded companies were acquired (or acqui-hired) before getting to Series A. CB Insights should be sending both over tonight.

But what we do have makes it clear that the Series A crunch is very real, and is unlikely to loosen up any time soon.

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