  The strong coupling of superconductivity to the orthorhombic distortion in
YBa2Cu3O7-d makes possible an analysis of the superconducting fluctuations
without the necessity of subtracting any background. The present
high-resolution capacitance dilatometry data unambiguously demonstrate the
existence of critical, instead of Gaussian, fluctuations over a wide
temperature region (+/- 10 K) around Tc. The values of the amplitude ratio
A+/A-=0.9-1.1 and the leading scaling exponent |alpha|<0.018, determined via a
least-squares fit of the data, are consistent with the 3D-XY universality
class. Small deviations from pure 3D-XY behavior are discussed.
