Place de l’analyse du mouvement dans un bilan de fertilité: Valeurs prédictives des différents paramètres mesurés

Resume

La fonction flagellaire est directement impliquée dans la rencontre des spermatozoïdes avec l’ovocyte et dans le processus de fécondation.

Les systèmes actuels d’analyse du mouvement spermatique permettent d’effectuer des mesures très rapides, qui pourraient en théorie être proposées à l’occasion de tout spermogramme. Néanmoins, les analyses de régression multiple montrent que si beaucoup de paramètres sont informatifs, ils le sont moins que certaines caractéristiques traditionnelles du spermogramme, comme le % de formes normales et le % de spermatozoïdes mobiles. Aussi, il nous paraît plus judicieux de sélectionner les indications de ce type d’analyse, comme un contexte de stérilité inexpliquée ou d'échec de FIV, afin de proposer la démarche thérapeutique la mieux adaptée; ainsi, une dyskinésie flagellaire révélée par une valeur très basse de l’amplitude latérale de la tête, ou par une vitesse de progression linéaire abaissée, représentera une bonne indication pour une technique de micro-injection, plutôt qu’une FIV traditionnelle.

Abstract

Routine evaluation of semen characteristics-spermiogram-includes estimation of the percentage of motile sperm; however it does not provide quantitative informations about sperm movement characteristics, except under the form of qualitative appreciations (slow, sluggish, yawing, non progressive, etc.). Flagellar function is indeed directly involved in the migration of spermatozoa through the female genital tract, and in the fertilization process by itself (migration through the zona pellucida requires special motility state, generally called “hyperactivation”). Sperm flagellar movements can now be indirectly investigated by analysing movements of sperm head, which are more easily detectable under phase contrast illumination: video signals are digitalized then sperm tracks are reconstructed by the computer from coordinates of sperm centroids (these systems are called “computer-assisted semen analysis” or “CASA”).

CASA systems are now so performing and rapid that sperm movement analysis (SMA) can be proposed in the same time of routine semen analysis. However SMA, together with other functional tests, offer more interest in some particular situations as unexplained infertility, or unexpected failure of IVF.

Numerous studies have tried to identify the most discriminant parameters, generally by means of multiple regression analysis. The interpretation of litterature data is difficult because of several differences in the protocol design, concerning either the measurements conditions (before or after sperm washing and selection) or the nature of the functional test: migration into cervical mucus, zona-free hamster egg penetration, IVF, etc. Moreover, the most discriminant factors are generally represented by classical parameters as % of normal forms or of motile sperm. In the present study we showed that only the factor “% of motility” allowed a significant discrimination according to different classes of fertilization rate (FR) in an IVF system. FR increased with hyperactivation rate (HA), but the statistical test was not significant. However, the more numerous cases of IVF failure were found in the group corresponding to very low HA rate (0–5%). We conclude that one major interest of SMA is to reveal some flagellar dyskinesia (i.e. corresponding to low values of amplitude lateral displacement of the head, or straight line velocity). These cases could then benefit of assisted reproductive techniques well adapted to this motion dysfunction, as subzonal insemination (SUZI) or intra-cytoplasmic sperm injection (ICSI).