Sandhya,
Congratulations on your pregnancy! You are in the golden middle trimester, if I am calculating right.
Your parents and your in-laws are adults who can and should think for themselves and handle their relationships including those with their child's in-laws. They should themselves decide how often they want to call, whether who initiates the calls is an issue or not. If any misunderstandings occur, they should sort it out themselves without bringing you and your husband into the picture. This is even more the case given that you do not live in India.
In other words - you shouldn't be telling your mother whether to call or not. Any temporary long distance tiffs you ever have with your in-laws shouldn't impact your parents relationship with them. You can give your mother a general guidance on what will be the best level of relationship to maintain, but not call by call instructions.
My opinion would be the same even if you had a rocky relationship with your in-laws.
-Rihana