Pregnancy rates with intrauterine insemination: comparing 1999 and 2010 World Health Organization semen analysis norms.

Over the past 30 years, The World Health Organization has serially measured norms for human sperm. In this study, 1999 and 2010 semen analysis norms as predictors of pregnancy were compared during intrauterine insemination (IUI). A retrospective cohort study was conducted using data collected from the Stanford Fertility Center, between 2005 and 2007, with 981 couples undergoing 2231 IUI cycles. Collected semen was categorized according to total motile sperm counts (TMSC): 'normal (N.) 1999 TMSC', 'abnormal (AbN.) 1999/N. 2010 TMSC', or 'AbN. 2010 TMSC'. Sample comparison was also based on individual semen parameters: 'N. 1999 WHO', 'AbN. 1999/N. 2010 WHO', or 'AbN. 2010 WHO'. Pregnancy (defined by beta-HCG concentration) rates were calculated. Data were compared using correlation coefficients, t-tests and chi-squared tests, with and without adjusting for confounders. Pregnancy rate comparison based on TMSC ('N. 1999 TMSC', 'AbN. 1999/N. 2010 TMSC' and 'AbN. 2010 TMSC') showed a negative correlation (r = -0.41, P = 0.05). Pregnancy rate did not differ when comparisons were based on the presence of abnormal parameters, even when controlling for confounders. Therefore, TMSC based on the 1999 parameters shows best correlation with pregnancy rate for IUI; updating these norms in 2010 has little clinical implication in infertile populations.