Is a double-embryo transfer detrimental to a patient's chances of pregnancy?.

Study question: How do pregnancy and birth outcomes differ between single (SET)- and double-embryo transfers (DET) when considering blastocyst quality? Summary answer: A high-quality embryo in a single transfer has better outcomes than in a double-embryo transfer with another embryo of any quality. What is known already: The transfer of multiple embryos in in-vitro fertilisation (IVF) was originally utilized to maximise rates of implantation and pregnancy; however, its use has subsequently led to a high risk of multiple pregnancy and its associated complications. It is also accepted that SET results in healthier babies. Although SET is typically preferred, a variety of factors may influence the decision to concurrently transfer a second embryo. The quality of embryos is one such factor, and it remains unclear how this may affect pregnancy outcomes. Study design, size, duration: This was a retrospective cohort study of 4275 single-embryo transfers and 881 double-embryo transfers in the blastocyst stage that occurred between 2005 and 2015. All SETs and DETs during this period were eligible for inclusion in the study (n = 72,867). Exclusion criteria included cases with missing data points (n = 10,564), duplicate transfers (n = 41,721), and transfers not utilising day-5 embryos (n = 8,715). Cases were also excluded where the quality of embryos was not adequate for our analysis (n = 6711) Participants/materials, setting, methods: Data was extracted from private IVF clinic database. To keep data independent, embryo transfers included in the study were limited to one per woman. An internal embryo quality grading system was used - Grade A (very good) to D (poor). Grade A SETs were compared with DETs with at least one Grade A embryo. Chi-square test used and crude odds ratios quoted. Logistic regression was performed with adjusted odds ratios, controlling for number of factors. Main results and the role of chance: We found that implantation, clinical pregnancy and live birth