O-144 Critical assessment of possible clinical benefits of culturing human embryos until day 7
Authors: Abdala A , Elkhatib I , Bayram A , El-Damen A , Melado L , Lawrenz B , Kalafat E , Fatemi H M , Nogueira D 
Published: June 2023

Abstract

Study question
Is there any benefit of extending culture until day (D) 7 to increase euploid blastocysts yield and clinical outcomes in a PGT-Aneuploidy analysis (PGT-A) program?

Summary answer
Extended culture until D7 increases euploid blastocysts yield and cumulative live birth. Highest benefit was observed in patients aged ≤41 with ≤2 D5/D6 blastocysts biopsied.

What is known already
It is well-known that female age is the strongest predictive factor of embryo aneuploidy and has been associated with delayed blastocyst development in vitro. Culturing embryos until D7 might increase biopsied blastocyst yields and euploidy outcomes among women undergoing ART as already been published. However, extended culture until D7 increases IVF workload and implies extra cost. It is unclear whether the practice is justified when a certain number of blastocysts have already been biopsied on D5/D6. Therefore, the additive value of extended culture until D7 needs further evaluation. Studies published in the literature have small sample sizes and are controversial.

Study design, size, duration
This single center observational study included 30,941 blastocysts from 6,976 consecutive IVF/ICSI PGT-A fresh autologous cycles performed between 2017 and 2022. Patients who underwent PGT-A by Next Generation Sequencing (NGS) were considered for the analysis. Only blastocysts graded ≥BL3CC (Gardner) that underwent TE biopsy on D5, D6 or D7 were included. Data were stratified by age categories (&lt;37, 37-41 and &gt;41) and on number of biopsied blastocysts performed on D5 and/or D6 of embryo culture.

Participants/materials, setting, methods
The additive value of extended embryo culture was assessed in terms of absolute numbers (percentage of D7 euploid blastocysts obtained) and theoretical benefit to cumulative live birth rate (having at least 1 live birth by using all available euploid blastocysts) as calculated by binomial density function. Results was assessed between female age strata (&lt;37, 37-41, &gt;41) and number of embryos biopsied in D5/D6 (No biopsy, ≤2, 3-4, 5-6 or ≥ 6 biopsied).

Main results and the role of chance
A total of 18,478 blastocysts were biopsied on D5 (38.5%), D6 (55.2%) or D7(6.3%). Euploidy rate decreased significantly for blastocysts biopsied on D5, D6 and D7 (55.6%, 39.7% and 27.1%, P &lt; 0.001, respectively). When stratifying patients by age, euploidy rates were consistently higher for D5 biopsied blastocysts compared to D6 and D7 (&lt;37: 61.1%, 50.0% and 38.5%, P &lt; 0.001; 37-41: 39.0%, 27.8% and 20.1%, P &lt; 0.001; &gt;41: 18.5%, 9.0% and 3.9%, P &lt; 0.001, for D5, D6 and D7, respectively). The chances of obtaining at least one euploid D7 blastocyst was higher among patients &lt;37 and 37–41 years compared to &gt; 41 years (7.2% and 4.4% vs. 0.6%, P &lt; 0.001). Among women &lt;37, a &gt; 25% increase in cumulative live birth rate (theoretical) was detected in 10.1% with no biopsy on D5/D6, 2.5% with 1-2 blastocysts biopsied on D5/D6 and only 0.3% with ≥3 blastocysts biopsied on D5/D6 (P &lt; 0.001). In older women (37-41), a &gt; 25% increase in cumulative live birth rate (theoretical) was found in 5.6% with no biopsy on D5/D6, 2.5% with 1-2 blastocysts biopsied on D5/D6, and only 0.4% with ≥3 blastocysts biopsied on D5/D6 (P &lt; 0.001). Women &gt;41 years rarely benefited from extended culture util D7 (&lt;1%) regardless of the number of blastocysts biopsied on D5/D6.

Limitations, reasons for caution
The study was based on a retrospective analysis data and results were calculated on a theoretical cumulative live birth. While this study provides one of the largest number of blastocysts analyzed in PGT-A and “freeze all” strategy, results should not be extrapolated to other populations or different ART routine practices.

Wider implications of the findings
Usable blastocysts (6.3%) and euploidy rates (27.1%) are significantly lower with D7 blastocysts compared to D5/D6 blastocysts. Patients aged &gt;41 do not benefit from extended embryo culture to D7 (&lt;1%). Culturing blastocysts for 7 days should be mainly decided based on the number of blastocysts biopsied on D5 or D6.

Trial registration number
not applicable