http://marginalrevolution.com/marginalrevolution/2005/03/women_iq_and_ma.html

In one study, four British Universities measured the IQ of 900 11-year-olds and revisited them 40 years later to see how their lives had moved on.

They found that the brighter girls were less likely to find a man who wants to marry them, with their chances diminishing dramatically in direct proportion to their level of intelligence.

For each 16-point rise in their IQ their marriage prospects dropped by 40%.

In contrast, boys' chances increased by 35% with each 16-point rise.

Source: http://www.sciencedirect.com/science/article/pii/S0191886904003137 - It's only the abstract, but I don't have access to the full article and it's pretty self explanatory.

Another important thing to note is that Mid-life social class had a similar association with marriage, with women in more professional jobs and men in more manual jobs being less likely to have ever-married by mid-life. Adjustment for the effects of mid-life social class and height on the association between childhood IQ and later marriage, and vice versa, attenuated the effects somewhat, but suggested that IQ, height and social class acted partly independently.

Hypergamy is discussed a lot, but I think this trend also has something to do with men not wanting to marry women that outearn/are smarter than them. Hypergamy is oft something that is "blamed" on women, but I think it goes both ways. Discuss.

EDIT: Thanks to /u/CFRProflcopter for finding the entire study. - http://eprints.gla.ac.uk/3134/1/childhood_iq.pdf