Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO₂ incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

Background: The standard scoring methodology, combined with blastocyst culture remains a valuable tool for embryo selection. Nevertheless, the embryo assessment based exclusively on morphological traits does not provide information about the chromosomal status of the embryo. Objective: The purpose of the present study has been to investigate the association between embryo morphology and chromosomal ploidy. Materials and methods: A total of 196 embryos resulting of 30 PGS cycles were biopsied on day 3 and tested for aneuploidies by comparative hybridization array. The embryos were classified into groups according to their morphology at zygote, cleavage and blastocyst stage. Results: Significantly statistical differences in embryo ploidy were observed when optimal day 3 morphology embryos were compared to medium morphology embryos (30.63% versus 17.28% respectively). A significantly higher proportion of euploid embryos were found in the group that achieved the blastocyst stage than in the arrested embryos group (42.57% versus 7.36%). Conclusion: The results provide evidence that embryo morphology and aneuploidy are linked both at day 3 and blastocyst stage. However the chromosomal status of the embryo may not be predicted relying exclusively on morphological assessment.