To explore the effects of chemical and physical parameters on embryo developmental competence, we conducted a systematic search on PubMed for peer-reviewed original papers using specific keywords and medical subject heading terms. Studies of interest were selected from an initial cohort of 4141 potentially relevant records retrieved. The most relevant publications were critically evaluated to identify the effect of these parameters on embryo development. Moreover, we generated a literature score (LS) using the following procedure: (i) the number of studies favoring a reference group was expressed as a fraction of all analyzed papers; (ii) the obtained fraction was multiplied by 10 and converted into a decimal number. We identified and discussed six parameters (oxygen, temperature, humidity, oil overlay, light, pH). Moreover, we generated a LS according to five different comparisons (37 °C vs. <37 °C; 5% vs. 20% oxygen; 5–2% vs. 5% oxygen; humidity conditions vs. dry conditions; light exposure vs. reduced/protected light exposure). Only two comparisons (37 °C vs. <37 °C and 5% vs. 20% oxygen) yielded a medium-high LS (8.3 and 7, respectively), suggesting a prevalence of studies in favor of the reference group (37 °C and 5% oxygen). In summary, this review and LS methodology offer semi-quantitative information on studies investigating the effects of chemical and physical parameters on embryo developmental competence.

Day 3 embryo quality is a predictor of in vitro fertilization (IVF) success rates in cleavage-stage embryo transfer. However, the association between day 3 embryo quality and clinical outcomes in blastocyst transfer policy is largely unknown. This retrospective study included 1074 frozen–thawed single day 5/6 blastocyst transfers between January 2019 and December 2022. Three groups were assessed depending on whether the transferred blastocyst derived from a top-quality, good-quality, or poor-quality embryo at day 3. The analysis was conducted independently for each blastocyst quality group (top, good, and poor) using multivariable logistic regression. We applied a Factorial Analysis of Mixed Data (FAMD) to reduce the potential collinearity between the covariates used in the model. All the blastocysts included in this study were obtained from the first ICSI freeze-all cycles. The cleavage and blastocysts stages were assessed between 67 ± 0.5 (day 3), 115 ± 0.5 (day 5), and 139 ± 0.5 (day 6) hours post-insemination (hpi), respectively. After adjusting for the day of transfer (day 5 or day 6) and FAMD dimensions, no statistical differences in a β-HCG, clinical pregnancy, and live birth were observed among the same-quality blastocysts derived from different day 3 embryo quality groups (top = A, good = B, and poor = C). Our findings showed that a day 3 embryo quality assessment may be unnecessary in planned freeze-all blastocyst cycles.

Despite advancements in technologies such as time-lapse microscopy and artificial intelligence, the gold standard for embryo selection still relies on standard morphological assessment. Several studies have investigated the correlation between blastocyst characteristics (expansion status, inner cell mass, and trophectoderm) and clinical outcomes, reaching contradictory results. In consideration of these ambiguities in the literature, we performed a retrospective study of 1546 untested first-vitrified–warmed single day 5/6 blastocyst transfers. The purpose of our study is to evaluate three scenarios: (i) independent association between each morphological characteristic (expansion status, inner cell mass, and trophectoderm) and live birth; (ii) comparison between blastocysts with inner cell mass grade A and trophectoderm grade B and blastocysts with inner cell mass grade B and trophectoderm grade A; and (iii) comparison between poor-quality day 5 and top-quality day 6 blastocysts. After adjusting for principal confounders, we report that trophectoderm is more predictive of live births than inner cell mass and expansion status. We observed a trend in favor of top-quality day 6 blastocysts over poor-quality day 5 blastocysts. Moreover, on the same day of development and expansion status, blastocyst BA should be preferable to blastocyst AB.