weight at conception

I've heard it from both sides that weight can or can't be in correlation to being able to conceive. I would like to know, am I alone in this? Should I focus more on weight loss than conception at the moment? I'm around 300lbs, I am aware that being pregnant and overweight comes with its own health concerns. Anyone else out there have their own stories to tell. I've been ttc for about 4 months.