Implantation: Embryo score to predict implantation after in-vitro fertilization: based on 957 single embryo transfers

Abstract

The purpose of this study was to devise an embryo score to predict the likelihood of successful implantation after in-vitro fertilization (IVF). Unlike most studies dealing with the influence of embryo stage and morphology on pregnancy, our study was based on single rather than multiple embryo transfers. A total of 957 single embryo transfers were carried out. No delivery was obtained after any of the 99 transfers using 1-cell embryos or embryos obtained after delayed fertilization. In the remaining 858 transfers, the embryos had cleaved. Higher pregnancy rates were obtained with embryos displaying no irregular cells (11.7 versus 6.9%; P < 0.01) and embryos displaying no fragmentation (11.5 versus 8.1%; P < 0.05). The 4-cell embryos implanted 2-fold more often than embryos with more or less cells (15.6 versus 7.4%; P < 0.01). Based on these observations, we devised a 4-point embryo score in which embryos are assigned 1 point each if they (i) are cleaved, (ii) present no fragmentation, (iii) display no irregularities, and (iv) have four cells. Both pregnancy rate and take home baby rate were significantly correlated with embryo score. Each point of this score corresponds to a 4% increase in pregnancy rate. Interestingly, pregnancy rate was significantly lower in women aged > 38 years (8.2 versus 11.4%; P < 0.05), even though embryo quality was similar regardless of age. Single embryo transfer allowed us to define a simple and useful embryo score to choose the best embryo for transfer to optimize IVF and embryo transfer outcome. The use of this embryo score could decrease multiple pregnancies after multiple embryo transfers.

An oocyte score for use in assisted reproduction

“…This is usually achieved either by the extended culture of human embryos to the blastocyst stage [5,6] or by the morphological analysis and selection of the highest quality embryos for transfer [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. More recently, the assessment of zygote quality has been applied [23][24][25][26][27][28][29][30][31][32].…”

Is the presence of a non-cleaved embryo on day 3 associated with poorer quality of the remaining embryos in the cohort?

“…Several studies have shown that a primary determinant of embryo viability is timing of onset of zygotic cleavage and entry into the first mitotic division [15,35,36]. Both animal and human studies have demonstrated that timely entry into the first cleavage (so called Bearly cleavage^) is associated with developmentally more competent embryos compared with late cleavage or no cleavage [37].…”

“…While recent studies have investigated the value of time-lapse imaging for embryo assessment and selection [reviewed by 6] standard morphological evaluation remains an important approach for evaluating embryo quality in IVF programs, particularly for those that lack time-lapse imaging systems. In addition, numerous studies have shown a direct correlation between the number of cells in a day 3 embryo and blastocyst formation [11][12][13][14], as well as implantation rates [15][16][17][18][19][20][21]. Indeed, several…”

“…studies have shown that cleavage rates that are either too slow or too fast are associated with a negative impact on implantation rate [15,18,21]. Moreover, arrested zygotes and slow cleaving embryos (two cells on day 2 or 3) are associated with higher rates of chromosomal abnormalities [22].…”

The impact of pronuclear orientation to select chromosomally normal embryos

“…Several non-invasive strategies can be used to improve end-results: pronuclei disposition, nucleolar organization (1-3), assessment of cell number, the morphological appearance at the time of transfer, and identification of normal-cleaving embryos with only mononucleate blastomeres without fragmentation (4)(5)(6)(7)(8)(9).…”