  Measurements of the specific heat jump at the onset of superconducting
transition in the iron-pnictide compounds revealed strong variation of its
magnitude as a function of doping that is peaked near the optimal doping. We
show that this behavior is direct manifestation of the coexistence between
spin-density-wave and superconducting orders and the peak originates from
thermal fluctuations of the spin-density-waves near the end point of the
coexistence phase -- a tetracritical point. Thermal fluctuations result in a
power-law dependence of the specific heat jump that is stronger than the
contribution of mass renormalization due to quantum fluctuations of
spin-density-waves in the vicinity of the putative critical point beneath the
superconducting dome.
