Does intracytoplasmic morphologically selected sperm injection improve embryo development? A randomized sibling-oocyte study.

STUDY QUESTION: Does high-magnification sperm selection influence oocyte fertilization and further embryo development?

SUMMARY ANSWER: The present study did not show a difference in oocyte fertilization rate, nor in embryo development between high-magnification intracytoplasmic morphologically selected sperm injection (IMSI) and conventional ICSI.

WHAT IS KNOWN ALREADY: The presence of nuclear vacuoles in sperm seems to influence embryo development and more specifically blastocyst formation. The use of high magnification for morphological sperm selection prior to ICSI has been associated with higher pregnancy rates and lower miscarriage rates.

STUDY DESIGN, SIZE, DURATION: A prospective sibling-oocyte study was conducted, including 350 ICSI cycles to alleviate male infertility. Cycles were included from March 2010 to November 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS: On the day of treatment, a high-magnification sperm morphology was assessed on at least 200 spermatozoa. Primary endpoints were oocyte fertilization rate and embryo development. Because embryo transfers were not randomized, the clinical outcome (clinical pregnancy rate per transfer cycle) was descriptive. However, the embryologist selecting the embryos for transfer was blinded for the sperm selection procedure.

MAIN RESULTS AND THE ROLE OF CHANCE: IMSI morphology was assessed in 330 semen samples, resulting in the following distribution: 18.1 ± 14.8% Grade I, 15.2 ± 10.3% Grade II, 12.3 ± 9.1% Grade III and 54.4 ± 23.2% Grade IV. Oocyte fertilization rate was 79.1 and 77.3% after IMSI and ICSI, respectively (NS, paired t-test). Embryo development was similar in both treatment groups up to Day 5 of preimplantation development. Comparable numbers of IMSI-only (n = 125) and ICSI-only (n = 139) embryo transfers were performed. Clinical pregnancies with fetal heart beat were equally distributed over transfers with embryos from IMSI-only (34.4%) or ICSI-only treatment (36.7%).

LIMITATIONS, REASONS FOR CAUTION: The clinical outcome remains descriptive. No firm conclusions could be drawn on cycle rank as a possible indication for IMSI.

WIDER IMPLICATIONS OF THE FINDINGS: The prevalence of vacuoles in normal-shaped spermatozoa is as low as 27.5%. A routine application of IMSI in unselected artificial reproductive technology patients cannot be advocated.

STUDY FUNDING/COMPETING INTEREST(S): None.