"Does delaying sex until after marriage improve your marital relationship? According to a 2010 research study, the answer is a clear yes. As reported in the Journal of Family Psychology (and later in the January 22, 2011, edition of The Economist), the study surveyed 2,035 married couples and asked them about their initial sexual experience together (before or after the wedding). Of the 2,035 couples, 336 couples reported waiting until they got married to have sex. The largest group of couples had sex within a few weeks of dating, and 126 couples had sex prior to dating. (This prompted a psychologist who reviewed the study to note, "I guess I'm not sure what constitutes dating anymore.")
After analyzing the data, the three researchers concluded that waiting until after marriage improved the relationship (for both men and women) in four key areas: sexual quality, relationship communication, relationship satisfaction, and perceived relationship stability.
According to the study, people who waited until marriage rated sexual quality 15 percent higher than people who had premarital sex rated relationship stability 22 percent higher rated satisfaction with their relationships 20 percent higher.
The data showed that premarital sex doesn't necessarily doom the future marriage to failure. On the other hand, based on this research, there is no validity to the idea that premarital sex is needed to "test" and possibly improve the future marriage relationship. The authors stated that waiting until after the wedding day (what they call "commitment-based sexuality") "is more likely to create a sense of security and clarity between partners … about exclusivity and a future."
Busby, D.M., Carroll, J.S., & Willoughby, B. J., "Compatibility or restraint? The effects of sexual timing on marriage relationships," Journal of Family Psychology (2010)