  We analyze the structure of 15 protocluster forming regions in the Milky Way
using their $1.3$ mm continuum emission maps from the ALMA-IMF large program.
The analysis of the clouds structure is performed using the delta-variance
spectrum technique. The calculated spectra display a self-similar regime on
small scales as well as the presence of a prominent bump on larger scales and
whose physical size, $L_{\rm hub}$, falls in the range of $\approx 7000$ au to
$60000$ au. These scales correspond to the sizes of the most compact clumps
within the protocluster forming clouds. A significant correlation is found
between $L_{\rm hub}$ and the surface density of the free-free emission
estimated from the integrated flux of the H41$\alpha$ recombination line
$\left(\Sigma_{\rm H41\alpha}^{\rm free-free}\right)$ as well as a significant
anti-correlation between $L_{\rm hub}$ and the ratio of the 1.3 mm to 3 mm
continuum emission fluxes $\left(S_{\rm 1.3 mm}^{\rm cloud}/S_{\rm 3 mm}^{\rm
cloud}\right)$. Smaller values of $\left(S_{\rm 1.3 mm}^{\rm cloud}/S_{\rm 3
mm}^{\rm cloud}\right)$ and larger values of $\Sigma_{\rm H41\alpha}^{\rm
free-free}$ correspond to more advanced evolutionary stages of the protocluster
forming clumps. Hence, our results suggest that the sizes of the densest
regions in the clouds are directly linked to their evolutionary stage and to
their star formation activity with more evolved clouds having larger
protocluster forming clumps. This is an indication that gravity plays a vital
role in regulating the size and mass growth and star formation activity of
these clumps with ongoing gas accretion
