A systematic review and meta-analysis came to the result that assisted zona hatching is related to increased rates of clinical pregnancy and multiple pregnancy in women with previous repeated failure or frozen-thawed embryos. However, it is unlikely to increase clinical pregnancy rates when performed in fresh embryos transferred to unselected women, to those without poor prognosis or to women of advanced maternal age.
^ abMartins, W. P.; Rocha, I. A.; Ferriani, R. A.; Nastri, C. O. (2011). "Assisted hatching of human embryos: A systematic review and meta-analysis of randomized controlled trials". Human Reproduction Update. doi:10.1093/humupd/dmr012.edit