Some tough lighting in this situation. The sensors in our digital cameras don't have the same dynamic range as our eyes, or that most film has, so it's easy to have highlights blown. Depending upon your equipment, with white wedding gowns, you could try underexposing a tad, with your exposure bias option. You might try setting it to under expose by 1/3 or 2/3 stops. With digital and post processing programmes, it's often easier to bring back shadow detail than trying to find digital information in blown highlights.
If you're shooting in manual mode, watch the light meter and try to have it under expose by that 1/3 or 2/3 stop.
Weddings are difficult, both technically and with dealing with people in a high stress condition. More power to you for tackling this!