3-Hydroxypropionaldehyde is formed by the condensation of acetaldehyde and formaldehyde.  This reaction, when conducted in the gas-phase, was the basis for a now obsolete industrial route acrolein: 
:CHCHO +  CHO →  HOCHCHCHO
:HOCHCHCHO  →  CH=CHCHO  +  HO
Presently 3-hydroxypropionaldehyde is an intermediate in the production of pentaerythritol.  Hydrogenation of reuterin gives 1,3-propanediol.