A comparative prospective study using matched samples to determine the influence of subnormal hypo-osmotic test scores of spermatozoa on subsequent fertilization and pregnancy rates following in-vitro fertilization.

The achievement of pregnancies in vivo is rare in couples where the male partner has defective sperm membranes as shown by hypo-osmotic swelling (HOS) test scores of < 50%. However, there have been mixed reports on the value of the HOS test in predicting outcome following invitro fertilization; some studies suggest reduced fertilization rates and others find little, if any, predictability of decreased fertilization. The assumption has been made that fertilization rates are proportional to pregnancy rates; however, this may not necessarily be true since defective spermatozoa could lead to a less viable pre-embryo and therefore a decreased viable pregnancy rate. We performed a comparative prospective study using matched controls to evaluate fertilization rates and to determine subsequent pregnancy rates. The mean HOS scores were 70.0 and 36.7% respectively, with mean motile sperm concentrations of 35.7 and 34.0 x 10(6)/ml in 27 matched pairs. There was no difference in the mean number of oocytes retrieved, fertilization rates or number of embryos transferred between the two groups by HOS score. The clinical and viable pregnancy rates and implantation rates were 25.9, 18.5 and 9.9% for normal versus 3.7, 3.7 and 1.1% for subnormal groups. These data suggest that low HOS scores may be associated with the formation of defective embryos, leading to low pregnancy rates but normal fertilization rates.