When to tell work I'm pregnant. Help!

Mckenzie
I just received an offer letter for a position with a new company, I am 12 weeks pregnant and have not yet told the company I am expecting. This wouldn't be as difficult if it wasn't for the industry I am in, as I manage alcohol brands. I know my pregnancy will not affect my work but considering this is a 95% male dominated industry, and drinking is an industry norm, I am afraid they will assume my pregnancy will affect sales. Should I err on the side of honesty and tell them before signing my offer letter? Or sign the letter and tell them before I start to really show? I just don't want to start off on the wrong foot and have them thinking I am dishonest and cannot be trusted. Thanks in advance for your help!