O-194 Blastulation timing in embryos is influenced by ploidy and is a predictor of transfer outcome
Authors: Abramov R , Madjunkov M , Librach C , Madjunkova S 
Published: June 2023

Abstract

Study question
Is there an association of the timing of blastulation (TE biopsy day) on embryo ploidy and pregnancy outcome after frozen embryo transfer?

Summary answer
Blastocysts expanded on day 5 are more likely to be euploid and result in an ongoing pregnancy after single euploid frozen embryo transfer (FET).

What is known already
Embryo selection for ET is commonly based on static morphological parameters for patients undergoing in vitro fertilization (IVF). Embryo quality on the day of biopsy in combination with preimplantation genetic testing (PGT) are considered important predictors for successful implantation. At present, coherent data regarding any association between the timing of blastulation with embryo ploidy and pregnancy outcomes following single FET are lacking. The aim of our study was to investigate the correlation of the culturing method and blastulation day (day 5/6/7) with embryo ploidy and outcomes of matched d5 vs d6 vs d7 FET cycles.

Study design, size, duration
This retrospective cohort study was performed at the CReATe Fertility Centre and its Reproductive Genetics Laboratory, between January 2019-December 2022. 29660 blastocysts from 5302 cycles (3645 patients) were analyzed using high resolution NGS PGT-A (10Mb resolution for copy number variations and 30%-70% for mosaicism). Pregnancy outcome data from 3942 single-FETs were analyzed. Average age of ovum provider was 32.9±5.8 and sperm provider 39.1±6.4. Clinical, laboratory and demographic data were obtained for statistical analysis.

Participants/materials, setting, methods
Embryos were allocated into four groups based on static morphological grading before biopsy on either d5 (n = 8312), d6 (n = 19183) or d7 (n = 2165): Good (&gt;1/2BB), n = 5648, Average (1BB, 2BB), n = 10492, Poor (&lt;1/2 BB) n = 12219 and Early blast, n = 1301. Embryo ploidy in each group and pregnancy outcomes from single euploid FET were compared between matched cycles of day 5 biopsy to days 6 and 7.

Main results and the role of chance
PGT-A analysis of 29660 embryos showed 53.1% were euploid, 33.9% were aneuploid and 13.0% were mosaic. There were significantly higher proportion of euploid embryos among those biopsied on d5 compared to d6 and d7 with average morphology grade (p = 0 O.R.=1.35979; p = 0.008098 O.R.=1.34442), poor (p = 0 O.R.=1.76481; p = 0 O.R.=2.73903) and early grades (p = 0 O.R.=2.71891; p = 0 O.R.=2.74271), but not among embryos with good grade (p = 0.244399 O.R.=1.07276; p = 0.182084 O.R.=1.38189).
Ongoing pregnancy rates were significantly higher for d5 vs d6 biopsied embryos, for all morphology grade groups: good (p = 0.030036 O.R.=1.26598), average (p = 0 O.R.=1.80782), poor (p = 0.000303 O.R.=1.89235) and early blasts (p = 0.049501 O.R.=3.30556). D5 blasts had higher ongoing pregnancy rates compared to d7 among average and poor morphology grade as well as early blast (p = 0.000419 O.R.=8.93182, p = 0.000036 O.R.=7.29464, p = 0.010034, respectively), except among good grade embryos (p = 0.885598 O.R.=0.9028). Continuous culture of embryos in Embryoscope™ versus conventional incubator did not influence the ploidy (n = 24321; n = 4756, respectively) or the pregnancy outcome after FET (n = 3134; n = 752, respectively) while comparing between each day of biopsy.

Limitations, reasons for caution
Although this is the largest sample size study to investigate the association of blastulation with ploidy and pregnancy outcomes, the sample size for d7 embryos is relatively low and results should be confirmed in a bigger study.

Wider implications of the findings
Prioritization of euploid embryos for transfer should consider the timing to blastulation and embryos biopsied on d5 should be considered before those biopsied on d6 or d7. This data has potential to shed light on the impact of normal chromosomal content on preimplantation embryo development.

Trial registration number
not applicable