Abstract
BackgroundBlastocyst development by extended culture in vitro allows the embryos to ‘select’ themselves, thus successful growth to the blastocyst stage is a reflection of the developmental competence of cleavage stage embryos in a cohort. The study aims to determine whether the number of frozen blastocysts is associated with live birth rates of the transferred fresh embryos.MethodThe retrospective study included 8676 cycles of first fresh embryo transfer from January 2016 to June 2019 at a fertility center of a university hospital. The patients with ≥ 10 oocytes retrieved were divided into three groups according to the number of frozen blastocysts: 0 (group 1), 1–2 (group 2), and ≥ 3 (group 3). The primary outcome measure was the live birth. The secondary outcome measures included clinical pregnancy rates and implantation rates. Logistic regression analysis was also performed.ResultsLive birth rates in patients with ≥ 3 and 1–2 frozen blastocysts were 47.6% and 46.1%, respectively, which were significantly higher than that in patients without blastocyst (36.0%). The clinical pregnancy rate in group 3 was 65.1%, which was also significantly higher than the other two groups (47.0% and 59.2%). The implantation rates were 35.5%, 47.6%, and 56.0% in the three groups, respectively (P < 0.001). Compared with groups of frozen blastocysts, 0 frozen blastocyst yielded a lower rate of live birth (the adjusted odds ratio: 0.526, 95% CI: 0.469, 0.612).ConclusionIn patients with optimal ovarian response that retrieved ≥ 10 oocytes, fresh embryos transfer followed by having blastocysts frozen is a strong indicator of pregnancy achievement, but the number of frozen blastocysts (if not = 0) has limited value in predicting live birth rates.
Highlights
As an independent factor for the success of in vitro fertilization (IVF) treatment, embryo quality is mainly evaluated by the morphological score including cell size, cell number, symmetry, percentage of fragments, defects of cytoplasm, and multinucleation [1,2,3,4]
Compared with groups of frozen blastocysts, 0 frozen blastocyst yielded a lower rate of live birth
In patients with optimal ovarian response that retrieved ≥ 10 oocytes, fresh embryos transfer followed by having blastocysts frozen is a strong indicator of pregnancy achievement, but the number of frozen blastocysts has limited value in predicting live birth rates
Summary
As an independent factor for the success of in vitro fertilization (IVF) treatment, embryo quality is mainly evaluated by the morphological score including cell size, cell number, symmetry, percentage of fragments, defects of cytoplasm, and multinucleation [1,2,3,4]. Apart from investigating the relationships between the quality of the transferred embryos and pregnancy outcomes, many studies have suggested that the quality of un-transferred or supernumerary embryos may be positively correlated with implantation rates [7,8,9,10]. These researches focused only on the number or quality of cleavage stage embryos. We are not aware of any data examining the correlation between the number of supernumerary blastocysts and live birth rates in fresh embryos transfers. The study aims to determine whether the number of frozen blastocysts is associated with live birth rates of the transferred fresh embryos
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