Objective: To evaluate the overall effect of assisted hatching (AH) on the implantation, pregnancy, and live birth rates in women undergoing intracytoplasmic sperm injection (ICSI)- cycles; and to determine the effect of AH on the cytogenetic outcome (chromosomal constitution) of pregnancy.Design: Prospective, randomized study.Setting: Academic research environment.Patient(s): A total of 172 couples were enrolled in the study.Intervention(s): Assisted hatching was carried out on day- 3 ICSI embryos.Main Outcome Measure(s): Implantation, clinical pregnancy, and live birth rates; cytogenetic analysis of abortuses and umbilical cord blood samples from newborns.Result(s): Biochemical, clinical, and ongoing pregnancy rates were not significantly different between the AH and control groups.The implantation rate was higher in the AH group than in the control group (16% vs.8% ), especially in women aged ≥ 35 years.Postnatal umbilical cord blood samples were collected and cytogenetically analyzed from 39 live births (20 from the AH group, 19 from the control group).Two abnormal karyotypes were found (one AH, one control).There were seven spontaneous losses during the study interval.Six of the abortuses underwent cytogenetic study (five AH, one control), and four were found to have an abnormal karyotype (three AH, one control). Conclusion: We found that AH improves implantation rates of ICSI cycles and seems to be most effective in women aged ≥ 35 years.A larger sample size is needed to determine whether AH improves the take- home- baby rate.Assisted hatching did not affect the rate of chromosomal abnormalities in live births in this study. Objective: To evaluate the overall effect of assisted hatching (AH) on the implantation, pregnancy, and live birth rates in women undergoing intracytoplasmic sperm injection (ICSI) - cycles; and to determine the effect of AH on the cytogenetic outcome (chromosomal constitution) of pregnancy. Design: Prospective, randomized study. Typing: Academic research environment. Patient (s): A total of 172 couples were enrolled in the study. Convention (s): Assisted hatching was carried out on day- 3 ICSI embryos. Main Outcome Measure (s): Implantation, clinical pregnancy, and live birth rates; cytogenetic analysis of abortuses and umbilical cord blood samples from newborns. Result (s): Biochemical, clinical, and ongoing pregnancy rates were not significantly different between the AH and control groups. The rate was higher in the AH group than in the control group (16% vs. 8%), especially in women aged ≥ 35 years. Postnatal umbilical cord blood samples were collected and cytogenetically anal .There were seven spontaneous losses during the study interval. Six of the abortuses underwent cytogenetic study (20 from the AH group, 19 from the control group). Two abnormal karyotypes were found (one AH, one control) five AH, one control), and four were found to have an abnormal karyotype (three AH, one control). We found that AH improves implantation rates of ICSI cycles and seems to be most effective in women aged ≥ 35 years. A larger sample size is needed to determine whether AH improves the take-home-baby rate. Assisted hatching did not affect the rate of chromosomal abnormalities in live births in this study.