[Gamete and embryo protection against oxidative stress during medically assisted reproduction]

So-called oxidative stress is due to the generation of reactive oxygen species (ROS), the most important of which are the superoxide anion (O2-*), hydrogen peroxide, and the hydroxyl radical OH*. ROS can damage gametes and embryos, through DNA (and RNA) fragmentation and membrane lipid peroxidation, potentially resulting in miscarriage. ROS are produced both physiologically (by oxidative metabolism) and in response to environmental factors such as oxygen, light, and traces of divalent cations. The body possesses several defense mechanisms against ROS, including antioxidant enzymes such as superoxide dismutase (SOD), catalase, glutathione peroxidase, and also small molecules like vitamins (A, C and E), glutathione and pyruvate. These different systems generally act in concert. Embryonic cells also possess DNA repair machinery. As oxidative stress is one of the main sources of embryo loss in vitro, it is important to protect both gametes and embryos against these insults during medically assisted reproduction.