Influence of the number of motile spermatozoa inseminated and of their morphology on the success of intrauterine insemination.

BACKGROUND

Although intrauterine insemination (IUI) is one of the most common assisted reproductive technology methods in the world, the relative influence of various semen characteristics on the likelihood of a successful outcome is controversial. The aim of our study was to assess the results of IUI as a function of both the number of motile spermatozoa inseminated (NMSI) and the percentage of morphologically normal spermatozoa after preparation.

METHODS

This was a retrospective study of 889 couples who underwent 2564 IUI cycles of ovarian stimulation with HMG or recombinant FSH in our centre between January 1991 and December 2000.

RESULTS

A total of 331 clinical pregnancies were obtained, for a pregnancy rate/cycle of 12.91%. When the NMSI was < 1 x 10(6), the pregnancy rate/cycle was significantly lower (3.13%) than in any of the subgroups with NMSI > or = 2 x 10(6). Sperm morphology, assessed before or after preparation, was not in itself a significant factor that affected the likelihood of IUI success. Nonetheless, when the post-migration rate of normal sperm was < 30%, the pregnancy rate/cycle was 5.43% when NMSI was < 5 x 10(6) and 18.42% when NMSI was > or = 5 x 10(6) (P = 0.008). Pregnancy rates did not differ significantly according to NMSI when the percentage of normal sperm after preparation was > or = 30%, or according to percentage of normal sperm when the NMSI was > or = 5 x 10(6).

CONCLUSIONS

Our results show that a minimum of 5 x 10(6) motile spermatozoa should be inseminated when the normal morphology of the sperm after preparation is < 30%; the quantity compensates at least in part for the defective quality. If this threshold of NMSI cannot be obtained, IVF should be recommended.