Chromatin packaging and morphology in ejaculated human spermatozoa: evidence of hidden anomalies in normal spermatozoa

This study aimed to investigate the association between anomalies in sperm chromatin packaging, morphology and fertilization in patients undergoing routine in-vitro fertilization (IVF) or subzonal insemination (SUZI). Sperm chromatin packaging was assessed using chromomycin A3 (CMA3), a fluorochrome specific for guanine-cytosine rich sequences of DNA. One hundred to 150 sperm cells were assessed in 55 patients to compare sperm chromatin packaging and morphology to fertilization after IVF or SUZI. When the morphology and CMA3 fluorescence of individual spermatozoa was assessed, > 75% of the macrocephalic sperm fluoresced in all patients. In contrast, a mean of 37% of the spermatozoa with normal morphology fluoresced in IVF patients compared with 58% of the normal spermatozoa in male factor patients treated by SUZI. SUZI patients displaying a high fluorescence (> 70%) in their spermatozoa also had a significantly lower fertilization rate. Lower packaging quality in morphologically normal spermatozoa may represent a major limiting factor in the fertilizing ability of male factor patients. This study confirms that a high percentage of CMA3 positivity is present in certain forms of male factor infertility and that such a test may be used to distinguish separate populations in morphologically normal spermatozoa.