Marriage is a life-changing decision and there is no shortage of books about how to best maintain your relationship post-wedding. But a new study suggests that the decisions you make before your wedding could largely influence the outcome of your marriage.

Researchers from the National Marriage Project at the University of Virginia studied over 1,000 unmarried Americans, ages 18 to 34, who have been in a relationship for five years. The report found that happy marriages may be based on the decisions people make before they say 'I do.'

When deciding to get married, couples are happier when more people celebrate the milestone with them. The researchers found that couples that invited at least 150 guests reported their marriage high quality. But when it comes to big weddings, the findings are focused on having family and friends that support you rather than amount of money spend.

"One possibility here is that couples with larger networks of friends and family may have more help, and encouragement, in navigating the challenges of married life." says W. Bradford Wilcox, professor of sociology and director of the National Marriage Project.

According to the findings, many couples now gradually move towards common goals rather than making definite decisions. For example, instead of making the decision to move in together, one partner may begin to spend the night and then subconsciously over time the couple finds themselves co-habitating.

"We believe that one important obstacle to marital happiness is that many people now slide through major relationship transition— like having sex, moving in together, getting engaged or having a child-that have potentially life-altering consequences," says Scott M. Stanley, co-author of the study and senior fellow for both the National Marriage Project and the Institute for Family Studies.

But the research suggests that couples that make definite decisions instead of sliding into transitions have better communication skills, a skill that is one of the building blocks of a healthy and happy relationship. Those who make decisions together tend to follow through with them.

"Our bottom-line advice to Americans hoping to marry is this: Remember that what you do before you say 'I do' may shape your odds of forging a successful marital future," says Stanley.