Purpose To determine whether the use of Magnetic Activated Cell Sorting (MACS) as a sperm selection technique improves ART success rates in couples undergoing assisted reproduction treatment. Methods Systematic review and meta-analysis of prospective randomized trials. Two reviewers conducted study selection and data extraction independently. Results Five studies (prospective randomized trials) that comprised 499 patients were included. Sperm selection using MACS resulted in statistically significant differences in pregnancy rates when compared with density gradient centrifugation and swim-up techniques (RR= 1.50, 95 % CI 1.14-1.98). No differences were found between the groups according to the implantation (RR= 1.03, 95 % CI 0.80-1.31) and miscarriage (RR=2. 00, rates. Conclusions MACS appears to be a safe and efficient method to select functional sperm with consistently good results. This technique may improve pregnancy rates when used to complement standard sperm selection methods in ART.

Purpose: To analyze the results of our transferred embryos, especially those that "changed" their blastomere nuclearity from Multinucleated (MN) to Mono-nucleated during development.Methods: Pregnancies where at least one MN embryo was transferred were retrospectively evaluated and categorized in order to record and follow-up on the ones that were implanted. Embryos were classified as normal (when all blastomeres were mono-nucleated on day one and two of development), corrected (multinucleated embryos on day one that became mono-nucleated on day two) and non-corrected (multinucleated either on day one, on day two or both days).Results: There were 633 transfer cycles analyzed. Thirtythree percent (206) had at least one embryo with a MN blastomere at a given stage of development. Pregnancy and implantation rates were 29.0% and 19.0% for the group of exclusively mono-nucleated embryo transfers, and 28.6% and 15.8% for the group with at least one MN embryo transferred. The pregnancy outcome for "corrected" and "noncorrected" embryos could be corroborated unequivocally in only 9 cases, with an outcome of 8 and 4 normal babies, respectively.Conclusions: Because the amount of data analyzed is not satisfactorily large, differences were not significantly different; however, a trend may exist showing that normal at term pregnancies obtained from corrected embryos are more likely to occur than those from non-corrected embryos. Nuclear observation on a daily basis should be one of the strate-Clínica de Fertilidad, Centro Médico Docente La Trinidad, Caracas, Venezuela e-mail: mgilco@cantv.net gies used to select the best embryos for transferring, to improve implantation rates and avoid multiple pregnancies.

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