It depends on what exactly you are referring to... see the sites below:
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=post-intervention+month&btnG=Google+Search&aq=f&oq=
What is pre-intervention and post-intervention month?
3 answers
It was about a study/research. So does it mean the month before the study and the month after?
Yes. The pre-intervention month is the month before you intervene in a situation. The post-intervention month must be the month following the end of the intervention. Check this site.
http://cat.inist.fr/?aModele=afficheN&cpsidt=19157804
http://cat.inist.fr/?aModele=afficheN&cpsidt=19157804