Low versus atmospheric oxygen tension for embryo culture in assisted reproduction: a systematic review and meta-analysis.

OBJECTIVE: To appraise the available evidence comparing low oxygen (LowO2) and atmospheric oxygen tension (AtmO2) for embryo culture. DESIGN: Systematic review and meta-analysis. SETTING: Not applicable. PATIENT(S): Women undergoing assisted reproduction using embryo culture. INTERVENTION(S): Embryo culture using LowO2 versus AtmO2. MAIN OUTCOME MEASURE(S): Reproductive, laboratory, and pregnancy outcomes. RESULT(S): A total of 21 studies were included in this review. All used O2 concentration between 5% and 6% in the LowO2 group. Considering the studies that randomized women/couples, we observed very low quality evidence that LowO2 is better for live birth/ongoing pregnancy (relative risk [RR] = 1.1, 95% confidence interval [CI] 1.0-1.3) and clinical pregnancy (RR = 1.1, 95% CI 1.0-1.2). Considering the studies that randomized oocytes/embryos, we observed low quality evidence of no difference of fertilization (RR = 1.0, 95% CI 1.0-1.0) and cleavage rate (RR = 1.0, 95% CI 1.0-1.1), and low quality evidence that LowO2 is better for high/top morphology at the cleavage stage (RR = 1.2, 95% CI 1.1-1.3). No studies comparing pregnancy outcomes were identified. Several studies used different incubators in the groups-a new model for the LowO2 group and an old model for the AtmO2 group. The risk of detection bias for the laboratory outcomes was high as embryologists were not blinded. CONCLUSION(S): Although we observed a small improvement (∼5%) in live birth/ongoing pregnancy and clinical pregnancy rates (PRs), the evidence is of very low quality and the best interpretation is that we are still very uncertain about differences in this comparison. The clinical equipoise remains and more large well-conducted randomized controlled trials are needed. They should use the same incubators in both groups and the embryologists should be blinded at least when evaluating laboratory outcomes.

N-Acetyl-Cysteine and l-Carnitine Prevent Meiotic Oocyte Damage Induced by Follicular Fluid From Infertile Women With Mild Endometriosis.

This study evaluated the potential protective effect of the antioxidants, l-carnitine (LC) and N-acetyl-cysteine (NAC), in preventing meiotic oocyte damage induced by follicular fluid (FF) from infertile women with mild endometriosis (ME). We performed an experimental study. The FF samples were obtained from 22 infertile women undergoing stimulated cycles for intracytoplasmic sperm injection (11 with ME and 11 without endometriosis). Immature bovine oocytes were submitted to in vitro maturation (IVM) divided into 9 groups: no-FF (No-FF); with FF from control (CFF) or ME (EFF) groups; and with LC (C + LC and E + LC), NAC (C + NAC and E + NAC), or both antioxidants (C + 2Ao and E + 2Ao). After IVM, oocytes were immunostained for visualization of microtubules and chromatin by confocal microscopy. The percentage of meiotically normal metaphase II (MII) oocytes was significantly lower in the EFF group (51.35%) compared to No-FF (86.36%) and CFF (83.52%) groups. The E + NAC (62.22%), E + LC (80.61%), and E + 2Ao (61.40%) groups showed higher percentage of normal MII than EFF group. The E + LC group showed higher percentage of normal MII than E + NAC and E + 2Ao groups and a similar percentage to No-FF and CFF groups. Therefore, FF from infertile women with ME causes meiotic abnormalities in bovine oocytes, and, for the first time, we demonstrated that the use of NAC and LC prevents these damages. Our findings elucidate part of the pathogenic mechanisms involved in infertility associated with ME and open perspectives for further studies investigating whether the use of LC could improve the natural fertility and/or the results of in vitro fertilization of women with ME.