If the Universe has the topology of a 3-torus (T³), then it follows from recent data on large-scale temperature fluctuations $ΔT/T$ of the cosmic microwave background that either the minimal size of the torus is at least of the order of the present cosmological horizon, or the large-scale $ΔT/T$ pattern should have a symmetry plane (in case of the effective T¹ topology) or a symmetry axis (in case of the effective T² topology), the latter possibility being probably excluded by the data.
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Alexei A. Starobinsky (1993) studied this question.