Study question Does body weight have any effect on clinical and perinatal outcomes in assisted reproduction techniques (ART)? Summary answer Obesity and overweight were associated with smaller oocytes retrieved and mature number, tendency to minor pregnancy rates, and with a greater chance of macrosomic newborns. What is known already The body mass index (BMI) is an international measure to categorize population regarding body weight. Overweight and obesity have an established negative impact on female fertility, especially due to chronic anovulation. However, studies are inconsistent regarding body weight and ART clinical and perinatal outcomes. Some say there is no difference, others show a little or unfavorable outcomes in overweight and obese patients. Study design, size, duration Retrospective cohort study performed at an assisted reproductive clinic. A total of 2296 follicle stimulation cycles were included, from 1686 patients, which resulted in 2278 embryo transfers (ET). Both fresh (1942) and vitrified (354) ET cycles were included in the study. The data refers to a period from 2013- 2020 and were collected from electronic records. Participants/materials, setting, methods Sample was divided into groups, according to BMI (kg/m²): Group 01 (<18.5, n = 30 cycles); Group 02 (18.5–24.9, n = 1630 cycles); Group 03 (25–29.9, n = 459 cycles) and Group 04 (≥30, n = 177 cycles). Data were presented as mean±SD, median (interquartile range), or percentage. ANOVA and Chi-square tests were applied, considering p < 0.05. Multiple logistic regression and generalized estimating equations were performed to consider patients and cycles. Main results and the role of chance The mean maternal age was 35.71±3.5 years old. A statistically significant difference was observed in retrieved oocytes and mature oocytes number (MII) when groups 01 and 02 were put together (G01+G02) and compared to groups 03 and 04: (8.8 [8.5–9.2] vs 7.9 [7.3–8.6] vs. 7.2 [5.9–8.4], p = 0.005) and (6.7 [6.4–7] vs 6 [5.5–6.5] vs. 5.3 [4.3–6.3], p = 0.003), respectively. A significant linear tendency to minor pregnancy rates with higher BMI (p = 0.038), with no significant difference in pregnancy rates was found between the four groups (52.6% vs. 47.9% vs. 46.7% vs. 36.3%, p = 0.124). There was no significant difference in cumulative pregnancy, live birth rate, fertilization and implantation rates between groups. Group 04 showed a higher, but not significant, prevalence of macrosomic newborns (p = 0.110). No statistical differences regarding any other clinical and perinatal outcomes were found (prematurity, intensive care unit admission, congenital malformations, Apgar index, newborn percentile, gestational age and birthweight. Limitations, reasons for caution This is a retrospective study with a limited number of patients. Also there was no information on patients’ weight gain throughout pregnancy, and others clinical pregnancy diseases that could affect perinatal outcomes. Wider implications of the findings: The study presented that the higher the weight, there seems to be a tendency towards worse outcomes of ART, especially regarding retrieved oocytes and mature oocytes number. Also, the study draws attention to the possible relationship between obesity and perinatal outcomes, also seen in spontaneous pregnancies. Trial registration number Not applicable

Study question Is there a correlation between Preimplantation Genetic Tests (PGT) results and Embryoscope’s KIDscore? Summary answer It seems that the higher the KIDscore, the higher the percentage of euploid embryos. What is known already Time lapse technology is bringing new perspectives in the relationship of embryos' morphokinetics and implantation rates after assisted reproduction techniques. However, it seems that only the embryo morphokinetics could be insufficient to predict euploidy. The KIDscoreTM D5 (KS5) algorithm, thus, is used for improving the implantation rates after a single euploid embryo transfer in its blastocyst stage and is related to higher rates of euploid embryos the higher the KS5, which could lead to higher implantation rates. Study design, size, duration Retrospective, observational study performed at a reproductive medicine center, using data collected between 2019 and 2021. A total of 802 embryos were included for analysis. Participants/materials, setting, methods All the embryos were biopsied for PGT (A, SR, and M), after being cultured for five or six days in an Embryoscope® time-lapse incubator (Vitrolife®, Canada). The embryos were then divided into three groups according to the KS5 evaluation: G1 (1-4), G2 (4.1-7), G3 (7.1-9.9) and the percentage of euploidy was evaluated in each group. For statistical analysis, Chi-square, and ANOVA tests, and Pearson correlation were used, considering p < 0.05. Main results and the role of chance The women’s mean age among groups G1 vs. G2 vs. G3 was, respectively: 39.1±3.5 vs. 38.7±3.3 vs. 37.6±3.8, p < 0.001; the mean KS5 of each group was: 2.9±0.7 vs. 5.4±0.8 vs. 8.0±0.7, p < 0.001 and finally, the euploidy rates comparing the G1 vs. G2 vs. G3 were, respectively: 98/341, 28.7% vs. 124/340, 36.5% vs. 63/121, 52.1%, p < 0.001. A weak correlation between women's age and KIDScore was also observed (-0.173, p < 0.001). Limitations, reasons for caution Although there is a positive correlation between embryomorphokinetics and euploidy, and the euploidy rate increases with higher KIDscore, only 50% of the high score embryos are euploids. Therefore, it is still important to perform embryo biopsy. Wider implications of the findings The findings suggest that better embryo morphokinetics provide greater chances of euploidy. Moreover, a weak negative correlation between women's age and KIDScore, possibly due to age-related aneuploidy, was observed. These results highlight time-lapse technology’s importance and the future perspective of morphokinetics evaluation improving implantation rates through euploidy identification. Trial registration number Not Applicable