Does Day 3 embryo status matter to reproductive outcomes of single blastocyst transfer cycles? A cohort study

To investigate whether Day 3 (D3) embryo status matter to reproductive outcomes of blastocyst transfer cycles.Retrospective cohort study.Assisted Reproduction Department of Shanghai Ninth People's Hospital, Shanghai, China.A total of 6906 vitrified-thawed single blastocyst transfer cycles in 6502 women were included.Generalised estimated equation regression models were used to calculate adjusted odds ratios (aOR) and 95% confidence intervals (CI) for the associations between embryo status and pregnancy outcomes.Biochemical pregnancy, miscarriage, live birth.High-quality blastocysts derived from poor-grade D3 embryos had comparable pregnancy outcomes to those derived from high-grade D3 embryos (40.0% versus 43.2%, aOR 1.00, 95% CI 0.85-1.17 for live birth rate; 8.3% versus 9.5%, aOR 0.82, 95% CI 0.63-1.07 for miscarriage rate). Cycles with low D3 cell number (five cells or fewer) had significantly higher miscarriage rate (9.2% versus 7.6%, aOR 1.33, 95% CI 1.02-1.75) compared with cycles with eight cells on D3.Poor-quality cleavage embryos should be cultivated to the blastocyst stage because high-quality blastocysts derived from poor-grade D3 embryos had acceptable pregnancy outcomes. When the blastocyst grade is identical, choosing embryos with higher D3 cell number (eight or more cells) for transfer could reduce the risk of early miscarriage.