P-511 Euploidy potential of day 7 embryos and the relevance in Assisted Human Reproduction treatments
Authors: Schuffner A , Francisquini C  D S , Giacomin S  A , Rosa V  B 
Published: July 2024

Abstract

Study question
Is it worth waiting embryos with late blastulation (Day 7) for preimplantation genetic analysis?

Summary answer
Embryo biopsy on Day 7 (D7) benefits cases of ovarian insufficiency and severe male factor with a euploidy rate of 15.1%.

What is known already
New technologies and improvements in IVF laboratories has allowed the extended cultivation of blastocysts to increase the pool of embryos per IVF cycle, resulting in greater chances, especially in cases of low blastulation rate, blastocysts with low quality or with few cells at Day 5(D5) and Day 6(D6). The variation in the time of the compaction stage depends on many factors, which may take more time, leading some embryos to reach the blastocyst stage only on D7 of development. These embryos have a lower euploidy rate, but there is embryonic competence and these embryos can be eligible for embryo transfer.

Study design, size, duration
Retrospective study that evaluated the chromosomal status (by Next Generation Screening - NGS) of 33 blastocysts biopsied on day 7 of development, between 2016 and 2023. Subsequently, it was compared the rate of euploidy and mosaicism with 295 blastocysts biopsied at D5 and D6, biopsied from January to October 2023. D7 embryos were originated from IVF cycles of couples with female age between 26 and 44 years, and males age between 29 and 56 years.

Participants/materials, setting, methods
D7 blastocysts from fresh and own oocytes fertilized by ICSI. The euploidy and mosaicism rates was compared, as well as the morphology of the ICM and trophectoderm (A-C; by Gardner Blastocyst Grade), the day which biopsy was performed and the respective infertility factors, in the groups: Group 1: D7 euploid and Group 2: D7 aneuploid. Subsequently, the rate of euploidy and mosaicism was compared between D7 embryos (Group 3) and D5/D6 embryos (Group 4).

Main results and the role of chance
There was no difference (p &gt; 0.05) between maternal age for group D7 euploid (38.4 years) vs group D7 aneuploid (37.9 years) and group 3 (38.4 years) vs group 4 (38.2 years). Embryonic morphological evaluation of D7 embryos showed that ICM was classified as B (18.2%) or C (81.8%) and trophectoderm as A (6.1%), B (24.2%) or C (69.7%). Comparisons of ICM and trophectoderm classifications between euploid (group 1) and aneuploid (group 2) in D7 blastocysts showed no difference (p &gt; 0.05). There was a predominance of 5CC embryos in both groups (Group 1: 40.0% vs Group 2: 42.4%), with no difference between them (p &gt; 0.05). In most cases, the biopsy was performed on two days (D5+D7 – 39.3%; D6+D7 – 35.7%), while in 10.7% of cases only on Day 7, when the infertility factor was 100% ovarian insufficiency. In cases of biopsy within 3 days (D5+D6+D7), we observed that 100% of cases were related to severe male factor. When comparing the euploidy rate of D7 embryos – group 3 (15.1%) with that of D5/D6 – group 4 (34.2%), we observed a statistical difference (p &lt; 0.05), while, for in mosaicism rates, D7 embryos represented 6.1% and D5/D6 embryos 9.1%, with no statistical difference (p &gt; 0.05).

Limitations, reasons for caution
The retrospective nature of our study may lead to bias derived from clinical practices and variability in relation to patient age, embryonic quality and infertility factor.

Wider implications of the findings
Extended culture and biopsy on D7 benefits cases of ovarian insufficiency and severe male factor by optimizing the IVF cycle. Although the euploidy rate in D7 embryos is lower than D5/D6 embryos, 15% of D7 embryos are euploid, demonstrating that the slower development is not caused exclusively by aneuploidy

Trial registration number
NA