Semen analysis and prediction of natural conception.

STUDY QUESTION Do two semen analyses predict natural conception better than a single semen analysis and will adding the results of repeated semen analyses to a prediction model for natural pregnancy improve predictions? SUMMARY ANSWER A second semen analysis does not add helpful information for predicting natural conception compared with using the results of a single semen analysis and addition of the second analysis to a prediction model for natural conception did not improve predictions. WHAT IS KNOWN ALREADY A major problem with semen analyses is the large variability of results within an individual. High-quality evidence is lacking on how many semen analyses need to be performed during the fertility workup to achieve an accurate prediction of conception. STUDY DESIGN, SIZE, DURATION We conducted a prospective cohort study of 897 consecutive couples presenting with subfertility in two university hospitals in the period 2002-2004 in the Netherlands. PARTICIPANTS/MATERIALS, SETTING, AND METHODS The laboratories scored sperm parameters according to the 1999 WHO criteria. Sperm concentration was counted and motility was assessed in a Makler counting chamber at a magnification of ×200. All assessments were performed by trained laboratory technicians. Follow-up started at the completion of the infertility workup and ended after 12 months. Primary end-point was natural conception resulting in an ongoing pregnancy. We constructed models for three strategies for the prediction of natural conception, using univariable and multivariable Cox hazard regression analyses. We evaluated the performance of the three strategies by comparing goodness-of-fit, discrimination and calibration. First, we analysed the semen parameters only. Secondly, we analysed the semen parameters in addition to the multivariable Hunault prediction model. MAIN RESULTS AND THE ROLE OF CHANCE Of the 897 couples, 132 (15%) achieved a pregnancy by natural conception. Using the results of a single semen analysis only, the calculated probabilities of natural conception within 12 months across the study population ranged from 0.12 to 0.38, with a median of 0.16 (IQR: 0.16-0.17). Using the results of two semen analyses did not lead to a better goodness-of-fit. Discriminative capacity was rather poor, with an area under the ROC curve (AUC) ranging from 0.51 to 0.56. Using the Hosmer-Lemeshow test statistic we found no signs of poor calibration. Using the results of two semen analyses in combination with the Hunault model did not significantly increase goodness-of-fit compared with using a single semen analysis. The Hunault model with the addition of the semen parameters fitted the data significantly better than the Hunault model itself (difference in -2 Log likelihood: 13; 3 df; P = 0.002). Using the Hosmer-Lemeshow test statistic we found no signs of poor calibration. LIMITATIONS, REASONS FOR CAUTION The academic setting possibly explains the relatively low natural conception rates, with only 15% achieving a natural conception within 1 year. Men with azoospermia were excluded. WIDER IMPLICATIONS OF THE FINDINGS Performing more than one semen analysis will not increase the prognostic power of the test in clinical practice. Adding the first semen analysis to the Hunault model for the prediction of natural conception improved performance significantly compared with using the Hunault model alone. External validation, in other populations, should follow to confirm our conclusions, and to evaluate the generalizability or transportability of the extended Hunault model. STUDY FUNDING/COMPETING INTEREST(S) No external funding was involved in this study. None of the authors has any conflict of interest to declare.