SuperWASP light curves for 53 W UMa-type eclipsing binary (EB) candidates, identified in previous work as being close to the contact binary short-period limit, were studied for evidence of period change. The orbital periods of most of the stars were confirmed, and period decrease, significant at more than 5 sigma, was observed in three objects: 1SWASP J174310.98+432709.6 (-0.055 pm0.003 s/yr), 1SWASP J133105.91+121538.0 (-0.075 pm0.013 s/yr) and 1SWASP J234401.81-212229.1 (-0.313 pm0.019 s/yr). The magnitudes of the observed period changes cannot be explained by magnetic braking or gravitational radiation effects, and are most likely primarily due to unstable mass transfer from primary to secondary components, possibly accompanied by unstable mass and angular momentum loss from the systems. If these period decreases persist, the systems could merge on a relatively short timescale.
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