DNA fragmentation in morphologically normal sperm is associated with decreased embryo quality and pregnancy outcome in ICSI treatment

Abstract

OBJECTIVE: Spermatozoa with normal morphological appearance are the cells that will be selected by the embryologist at the time of oocyte injection for ICSI. The objectives of this study were to evaluate the presence of DNA fragmentation in morphologically normal sperm in an aliquot of the same sample used for ICSI; and to correlate DNA fragmentation of morphologically normal sperm with embryo quality and pregnancy outcome. DESIGN: Prospective study. MATERIALS AND METHODS: 36 semen samples were subjected to separation by swim-up and the standard semen parameters were evaluated. From the same sample used for ICSI, a small fraction was allocated to the evaluation of sperm DNA fragmentation and morphology in the same sperm cell, using TUNEL assay and strict criteria by phase contrast. On the day of embryo transfer, embryo quality (EQ) (cleavage and morphology) was assessed. An individual EQ score was calculated by multiplying the number of blastomeres times the morphology grade. A cumulative score was calculated by adding the EQ scores of all individual embryos and was then divided by the number of embryos. A clinical pregnancy was established by ultrasound detection of fetal heartbeat at 7 weeks. RESULTS: The age of women (33.2±1.3 years vs 34.8±0.9 years, P>.05), the percentage of total sperm with TUNEL positivity (12.9±2.3% vs 15.0±2.5%, P>.05), and the percentage of normal sperm morphology (2.4±0.6% vs 1.5±0.2%, P>.05) was not statistically different in pregnant versus non-pregnant cycles. No correlation was found between the percentage of total sperm with TUNEL positivity and the percentage of normal sperm with DNA fragmentation. A negative correlation was found between the percentage of morphologically normal sperm with DNA fragmentation and EQ, for the total of embryos (r=-0.594, P<.001) as well as for the transferred embryos (r=-0.617, P<.001). The percentage of normally shaped sperm with DNA fragmentation was significantly different between pregnant and non-pregnant cases (18.9±8.6% vs 33.8±4.0 %, P<.05). CONCLUSIONS: Results demonstrate a clear association between morphologically normal spermatozoa with DNA fragmentation and poor embryo quality and reduced pregnancy outcome in ICSI patients. Sperm normal morphology alone cannot be used as a unique attribute for the selection of sperm for ICSI. New methods that allow an accurate separation of viable sperm with intact DNA should be sought for optimizing ICSI outcome.