In the last years, we have started to spatially resolve the small gas and dust condensations in multiple star-forming (MSF) regions that will eventually become a massive star or system. We call these condensations "cores", with sizes on the order of 0.01 pc. By constructing the Core Mass Function (CMF) of a region and comparing it with the IMF, we can attempt to determine the evolutionary process from core to star, but for MSF regions, the relationship between the CMF and the IMF is not yet well understood. This is, among other factors, due to the fact that there are not many MSF CMFs determined. Those few that are, seem to tell a story of evolution by presenting slopes varying from that of the Salpeter IMF to very different values. But are we in fact observing regions at different evolutionary stages? One way to address that is by determining the deuteration fraction of those regions, since deuterated species are first released into the gas medium and then destroyed at the early stages of evolution.
