Clinical outcomes of Day-7 blastocysts: a systematic review and meta-analysis

BACKGROUND: Extended embryo culture beyond Day-6 remains controversial. While a small subset of embryos reaches the blastocyst stage on Day-7, their developmental competence and reproductive potential remain uncertain. Data from previous studies have been limited and heterogeneous, particularly for meta-analytical evaluation of euploid embryo transfers. OBJECTIVE AND RATIONALE: This systematic review and meta-analysis compared clinical pregnancy (CPR) and live birth rates (LBR), as well as implantation (IR), miscarriage (MR), and ongoing pregnancy rates (OPR), between Day-7 frozen blastocysts and those obtained on Day-5 and/or Day-6. Euploidy rates by day of blastocyst development and available perinatal outcomes were also assessed. SEARCH METHODS: Conducted according to PRISMA guidelines, this review included full-length English-language human studies, published up to 1 April 2026, comparing frozen transfers of Day-7 versus Day-5/6 blastocysts and reporting at least clinical pregnancy and/or live birth outcomes. Random-effects models were used to estimate pooled odds ratios (ORs) with 95% confidence intervals (95% CI). Obstetric and perinatal outcomes were analysed when available. OUTCOMES: A total of 17 retrospective studies were included. Across 2908 Day-7 transfers, CPR and LBR were significantly lower than for Day-5 (CPR: OR 0.26, 95% CI 0.19-0.35, I2: 76.2%, 16 studies, 2799 and 34 442 transfers at Day-7 and Day-5, respectively; LBR: OR 0.23, 95% CI 0.16-0.33, I2: 76.3%, 12 studies, 2687 and 31 630 transfers at Day-7 and Day-5, respectively) and Day-6 blastocysts (CPR: OR 0.38, 95% CI 0.31-0.48, I2: 54.4%, 16 studies, 2799 and 28 563 transfers at Day-7 and Day-6, respectively; LBR: OR 0.37, 95% CI 0.28-0.49, I2: 60.2%, 12 studies, 2687 and 26 687 transfers at Day-7 and Day-6, respectively). Similarly, IR and OPR were significantly lower in the Day-7 group than in the Day-5 or Day-6 groups, while MR was higher compared with Day-5 blastocysts (OR 1.54, 95% CI 1.04-2.30, I2: 51.1%, 14 studies, 685 and 18 609 pregnancies at Day-7 and Day-5, respectively). When considering only PGT-A euploid blastocysts, CPR and LBR remained significantly lower in the Day-7 group compared with Day-5 (CPR: OR 0.21, 95% CI 0.14-0.33, I2: 58.0%, 7 studies, 365 and 7064 transfers at Day-7 and Day-5, respectively; LBR: OR 0.21, 95% CI 0.17-0.28, I2: 0%, 6 studies, 364 and 5924 transfers at Day-7 and Day-5, respectively) and Day-6 (CPR: OR 0.36, 95% CI 0.28-0.46, I2: 40.8%, 7 studies, 365 and 4617 transfers at Day-7 and Day-6, respectively; LBR: OR 0.36, 95% CI 0.28-0.46, I2: 0%, 6 studies, 364 and 3782 transfers at Day-7 and Day-6, respectively), and MR was higher than Day-5 (OR 2.78, 95% CI 1.57-4.89, I2: 32.4%, 6 studies, 95 and 4018 pregnancies at Day-7 and Day-5, respectively). Euploid rates were also significantly reduced for Day-7 blastocysts compared with Day-5 and Day-6. Data on perinatal outcomes were limited but overall reassuring. The pooled analyses revealed low to high heterogeneity across studies. WIDER IMPLICATIONS: Despite lower success rates, including for euploid embryos, Day-7 blastocysts may still contribute to cumulative live birth rates, notably in poor-prognosis patients. Prospective studies are needed to better assess perinatal and long-term outcomes. REGISTRATION NUMBER: PROSPERO (CRD420251114251).