MY INTERVIEW DATE COLLIDES WITH MY DELIVERY DATE HELP!!!

Please how do I go about this, my interview date collides with my expected delivery date. My plan was to have my baby over there where my husband resides but the date came rather late.

Should I write to them to postpone the interview data or should I wait till its close to my delivery and what duration will it take them to reschedule another interview date with me?  

HELP!!!!!!!!!!!!!!!!!!

I am a caterer,i ave been for 8 years,so i apply for a b1/b2 visa so i can attend a catering conference in Philadelphia called THE ART OF FOOD CATERING,i ave been refused twice now,the 1st time was 15th of July 2013,i was so downcast and decided to try again,i got another date for 29th of July and was refused, I am so so downcast and i really need to attend that conference to help my business.

my question is, I have been able to get a date for 1st week in august again,and the conference is on the 11th of august,do you think i will appear desperate and be refused?