Morphological parameters of the blastocyst to predict embryo quality: a systematic review and meta-analysis

In assisted reproductive technology (ART), the morphological assessment of blastocyst quality is the crucial step that determines the success of embryo transfer. But the relative importance of three blastocyst components-blastocyst expansion (EH), inner cell mass (ICM), and trophectoderm (TE)-for embryos is still a matter of controversy. Therefore, the aim of this meta-analysis is to compare and rank the effects of blastocyst scoring on producing live births.

We systematically searched CINAHL, Cochrane, Embase, MEDLINE, PubMed, Scopus, and the Chinese Medicine database from inception to February 26, 2023. This research includes original articles reporting neonatal outcomes after in vitro fertilization (IVF)/ intracytoplasmic sperm injection (ICSI) embryo transfer which contained definitive grading of EH, ICM, and TE characteristics at the blastocyst stage using the Gardner scoring system.

We conducted a meta-analysis of 33 studies encompassing 42,974 ART embryos from 46,099 infertile women, with 19 studies reporting live births in 28,918 women involving 30,651 embryos. The analysis revealed that embryo components were ranked by their suitability for live births, with TE (A) scoring highest, followed by ICM (A) and EH (5), while EH was the least favorable. The most favorable embryo morphologies for higher live birth rates were 5AA, 4AA, 6AA, 5AB, 3AA, 5BA, 4AB, 2AA, and 4BA, with 1CC being the least unfavorable.

Morphological assessment of embryo quality serves as a crucial protocol in the selection of high-quality embryos after ART, and our study may provide a guideline to assist in the selection of high-quality embryos.