A New Day 4 Grading System to Assess Embryo Quality in Frozen Embryo Transfer Cycles
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REPRODUCTIVE BIOLOGY: ORIGINAL ARTICLE
A New Day 4 Grading System to Assess Embryo Quality in Frozen Embryo Transfer Cycles Hong-Xing Li 1,2
&
Xiao-Juan Xu 1,2 & Lin Liu 1,2
Received: 26 March 2020 / Accepted: 8 November 2020 # Society for Reproductive Investigation 2020
Abstract To present a new day 4 (D4) embryo grading system to assess embryos in frozen–thawed embryo transfer (FET) cycles. A new grading system (grades A–E) was developed from the 2011 ESHRE Istanbul Consensus for D4 embryos in FET cycles. Embryos with complete compaction were classified as grade A; those with partial compaction were assigned as grade B; and those without compaction were classified as grades C, D, and E according to their different blastomere number ratio (BNR; number of embryo blastomeres on D4/ number of embryo blastomeres on D3, D4/D3). Embryos with a BNR of ≥ 1.5 were defined as grade C, those with a BNR of ≥ 1.2 and < 1.5 were defined as grade D, and those with a BNR of ≥ 1.0 and < 1.2 were defined as grade E. Using this proposed grading model, 5460 embryos with known implantation data were retrospectively analyzed after D4 transfer in FET cycles. The transferred embryos exhibited a similar declining trend in implantation and live birth rates from the top grade A to the lowest grade E. The in vitro fertilization group showed increased implantation rates of grade B and E embryos compared with the intracytoplasmic sperm injection group (grade B: 41.99%, 34.63%, χ2 = 5.84, p < 0.05 and grade E: 18.98%, 14.08, χ2 = 75.62, p < 0.01). Receiver-operating characteristic analysis revealed that our proposed model predicted the implantation outcomes and live birth rates of all embryos (area under the curve = 0.65; 95% confidence interval [CI],0.63–0.66; p < 0.01 and AUC = 0.73; 95%CI, 0.65–0.84; p < 0.001, respectively). This study demonstrates that the new grading system provided by us can be a useful tool for assisting embryo selection via changes in embryo morphology. D4 embryo transfer provides a simple and applicable method for FET cycles in daily practice. Keywords Embryo . Grading system . Implantation . Compaction
There have been significant advances in the development of the in vitro fertilization–embryo transfer (IVF–ET) technology since the first IVF baby was born in the 1970s. Although there have been continuous improvements in the technology of embryo culture in vitro, there is still a lack of objective as well as accurate methods for judging embryo quality, which is an important factor affecting the outcome of clinical pregnancy [1, 2]. To date, no consensus exists on the classification of the quality of day 4 (D4) embryos in frozen embryo transfer (FET) cycles. Because embryos are usually frozen on D3, we have routinely cultured embryos overnight for transfer on D4 in FET cycles. However, it is extremely challenging to select
the most viable and potent embryos for D4 ET so as to reduce the number of transplanted embryos while improving the ability of embryo implantation. This study aimed to present a new grading sy
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