Standardisation de la classification morphologique des spermatozoïdes humains selon la méthode de David modifiée

Abstract

It has now been clearly established that the percentage of morphologically normal sperm and the level of several specific anomalies of spermatozoa have a prognostic value in vivo and in vitro. Assessment of human sperm morphology therefore represents an essential step in routine semen analysis. Smears, preferably stained by the Shorr technique, are examined at a final magnification of ×1000 (×100 objective with oil immersion and ×10 ocular lens). David's method for classification of morphological anomalies of human spermatozoa was proposed in the mid-seventies and was modified in the early nineties to account for all of the defects known to interfere with normal sperm functions. This method has been adopted in France by the vast majority of public and private laboratories. It allows classification of seven anomalies of the head: tapered, thin, microcephalous, macrocephalous, multiple, abnormal or absent acrosome, abnormal postacrosome, three anomalies of the midpiece: cytoplasmic droplet, thin, bent, and five anomalies of the principal piece: absent, short, irregular, coiled and multiple. The originality of the method is to account for all combinations of anomalies found for each abnormal sperm by means of a multiple entry system. Since there is no objective reason to favour certain anomalies over others, all anomalies found for each abnormal sperm should be recorded using a systematic procedure: description of the head, followed by the midpiece, and lastly the principal piece. The multiple anomalies index or MAI is calculated. This index, which is a direct application of the multiple entry system, corresponds to the mean number of anomalies per abnormal sperm (the ratio of the total number of anomalies to the number of abnormal sperm). Several studies have indicated the prognostic value of MAI, and calculation of the MAI is recommended in the WHO manual on semen analysis. Unfortunately, the morphological assessment of human spermatozoa which appears simple at a first glance, raises a number of real difficulties: this microscopic analysis is highly subjective by nature and no uniform recommendations for staining technique and classification have yet been defined. Internal and external quality control schemes have revealed the marked intra- and interindividual variability of the results, which in turn have important consequences on the reliability of the analysis and the management of infertile couples. All steps of the procedure, from preparing the smear to writing the examination report must therefore be standardised. The present article focuses on standardisation of the classification step using David's method. Precise descriptions of the anomalies found by conventional microscopy and their ultrastructural substratum are presented, together with practical recommendations for the classification of sperm defects and calculation of the MAI.