Abstract
BackgroundTo determine whether the embryo developmental stage affects biochemical or clinical pregnancy loss in young women undergoing frozen-thawed embryo transfer (FET) and to investigate the underlying mechanism.MethodsThis was a retrospective study including a total of 18,34 β-HCG (human chorionic gonadotropin)-positive FET cycles. According to the morphological appearance (MA) of transferred blastocysts, FET cycles with blastocysts were divided into two groups: Group A: morphologically good (MG) blastocysts only, and Group B: at least one morphologically non-good (MNG) blastocyst. FET cycles with day 3 cleavage embryos were assigned as Group C. Biochemical and clinical pregnancy loss were the main outcome measures.Result(s)We predicted 78% in vivo-formed MG and 53.9% in vivo-formed day 5 blastocysts in Group C. (a) Including cases in Group A and Group B for binary logistic regression, we showed that Group B and day 6 blastocysts had significantly higher rates of BPL and CPL than Group A and day 5 blastocysts, respectively. (b) Including cases in Group A, Group B, and Group C for binary logistic regression, we showed that Group C had a significantly higher rate of BPL than Group A and day 5 blastocysts and a similar rate of BPL as Group B and day 6 blastocysts. Group C had a higher rate of CPL than Group A (p=0.071) and day 5 blastocysts (p=0.039), and a lower rate of CPL than Group B (p=0.199) and day 6 blastocysts (p=0.234).Conclusion(s)(1) MA and days of usable blastocysts could serve as independent factors affecting the occurrence of BPL and CPL. (2) Transfer of day 3 cleavage embryos may produce “unusable blastocysts” in vivo, which significantly increased the rate of BPL. (3) The rate of CPL resulting from the transfer of day 3 embryos may depend on the rate of in vivo-formed MG or day 5 blastocysts. Our study indicated that the difference in the BPL or CPL between transfer of blastocysts and day 3 cleavage embryos may largely depend on the quality of embryos transferred.
Highlights
Would blastocyst transfer result in reduced pregnancy loss (BPL or clinical pregnancy loss (CPL)) compared to Day 3 cleavage embryo transfer?
According to the in vitro cultural data of Day 3 cleavage embryos, the ratio of usable morphologically good (MG) blastocysts formed from grade I embryos was 88.9%, from grade II embryos was 78.5%, and from grade III embryos was 45.7%, while the ratio of usable Day 5 blastocysts formed from grade I embryos was 62.7%, from grade II embryos was 54.2%, and from grade III embryos was 28.9% (Table 5)
We predicted that 78% of in vivo-formed MG blastocysts and 53.9% of in vivo-formed Day 5 blastocysts resulted from the transfer of Day 3 cleavage embryos in the present study (Table 6)
Summary
The fertilized zygote develops into a Day 3 cleavage embryo, which further becomes a blastocyst. With successful implantation and subsequent further development, gestational sacs can be found by ultrasound examination, indicating the achievement of clinical pregnancy. Biochemical pregnancy loss (BPL) or clinical pregnancy loss (CPL) often occurs during pregnancy, resulting in a failed pregnancy [3, 4]. Day 3 cleavage embryos were the most commonly used for transfer in in vitro fertilization (IVF). In recent years, extended culture of Day 3 embryos to the blastocyst stage has been widely adopted in most reproductive centers worldwide. Would blastocyst transfer result in reduced pregnancy loss (BPL or CPL) compared to Day 3 cleavage embryo transfer?. To determine whether the embryo developmental stage affects biochemical or clinical pregnancy loss in young women undergoing frozen-thawed embryo transfer (FET) and to investigate the underlying mechanism
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