from what i understand, for the preggy is ok, but the thing is the couple, as long as newly wed don't mind, it is ok for preggy to attend. Cos supposedly, pregnant woman is "stronger" than the newly wed and will sort of suppress the "xi qi" of the newly wed, so some newly wed or parents will mind. I have informed one of my friends that I am preggy and if she is ok, she was rather straight forward to tell me that her parents will mind and so she chose not to send invitation to me which both of us are ok with that.
For full month, my CL told me that you have to inform the parents if they feel that the baby is the pantang kind, they will not invite you. But actually as long as preggy carry the newborn, they will not be afraid anymore. Cos the pantang saying goes that newborn are petty towards the unborn child and will cry a lot after they saw the pregnant lady but once you carry the baby, they will not be petty already (cos share love ah). Well, depending on how pantang the other party is.