Bigelow, J. L., Dunson, D. B., Stanford, J. B., Ecochard, R., Gnoth, C., & Colombo, B. (2004). Mucus observations in the fertile window: a better predictor of conception than timing of intercourse. Human Reproduction (Oxford, England), 19(4), 889–892.
Key Results
There was a strong increasing trend in the day-specific probabilities of pregnancy with increases in the mucus score. Adjusting for the mucus score, the day-specific probabilities had limited variability across the fertile interval.
Conclusion
Changes in mucus quality across the fertile interval predict the observed pattern in the day-specific probabilities of conception. To maximize the likelihood of conception, intercourse should occur on days with optimal mucus quality, as observed in vaginal discharge, regardless of the exact timing relative to ovulation.