Using High Magnification to Select Sperm: a Large Prospective Cohort Study Comparing ICSI and IMSI

Purpose: To compare two methods for the observation and selection of spermatozoa before microinjection. Methods:We analyzed 9012 treatment cycles-3339 cycles of intracytoplasmic sperm injection (ICSI) (37.1%) and 5673 cycles of intracytoplasmic injection of morphologically selected spermatozoa (IMSI) (62.9%)-for fertilization, pregnancy, live birth, and miscarriage rates.The primary endpoints were clinical pregnancy rate and live birth.Secondary endpoints were fertilization, blastulation, and miscarriage rates. Results:In the ICSI group, 530 cycles (15.9%) ended with no embryos appropriate for transfer or freezing, versus 426 cycles (7.5%) in the IMSI group (P < 0.01).After correction for age, body mass index, anti-Müllerian hormone level, and number of previous treatments, IMSI cycles were more likely to end in a pregnancy (odds ratio [OR] 1.17, P = 0.009).When the cohort was adjusted according to total motile sperm count, IMSI performed particularly well in cases with severe oligozoospermia: 70% more pregnancies (OR 1.68, 95% confidence interval [CI] 1.19-2.35)and twice as many live births (OR 2.05, 95% CI 1.36-3.08)compared with ICSI.The miscarriage rate was also significantly lower using IMSI (13.5%) than with ICSI (23.2%) (P = 0.03). Conclusion:We recommend that IMSI be considered immediately in cases of severe male factor infertility, and as a second-line approach in cases of ICSI failure.