P-243 Effect of delayed development of embryos 7 days on embryo quality, ploidy and reproductive cycle outcomes
Authors: Chernoshtan K , Koloda E , Lelyavina A , Gorelova I , Makolkin A , Ganzhina A 
Published: July 2024

Study question

How does delay in embryo development before Day7 affect blastocyst quality, ploidy and reproductive cycle outcomes?

Summary answer

Embryo quality and ploidy are statistically significantly lower in the Day7 group, no difference in implantation rate was found.

What is known already

In clinics that allow extended culture up to Day7, on average 5% of embryos have a 48-hour delay in development, blastulation occurs on the 7th Day (Hammond et al., 2018). Day7 blastocysts may have good morphology and be euploid, give a pregnancy and birth of a healthy baby. Back in 2013 it has been proven that embryos from patients over 35 years of age take longer to form a blastocyst (Shapiro et al., 2013). Cultivation until Day 7 is justified for couples with a poor prognosis in cycles.

Study design, size, duration

This was a retrospective cohort study in a private Delta Fertility Clinic of consecutive female infertility patients (n = 422) between Sept 2021 and Sept 2022. Average age of the patients was 39,7 years who underwent frozen embryo transfer (FET) of a single euploid day 5, 6 or 7 blastocyst. Then we compared the outcomes in the 5, 6 and 7 Day groups.

Participants/materials, setting, methods

The results of culture and subsequent biopsy of trophoectoderm with PGT-A of 2095 blastocysts (1516 were tested with PGT-A) in 482 cycles were analyzed, of these, embryos Day7 suitable for biopsy were 9.8% (149). Blastocysts were classified as good (AA/AB/BA/BB) or poor (AC/BC/CA/CB) (Gardner D.K. et al., 1999). Cultivation performed in single drops, biopsy was performed using the flicking method. Statistical analysis was performed using the Pearson’s Chi-Squared Test.

Main results and the role of chance

In 3.4% of cases, patients had only Day7 blastocysts. Poor quality blastocysts were predominant in D7 blastocyst group (good quality: 91.0%, 65.2%, 46.3%; poor quality: 9.0%, 34.8%, 53.7%, P &lt; 0.001 for D5, D6 and D7 blastocysts; respectively). The number of euploid embryos was significantly lower in the Day 6 and Day 7 group compared to Day 5 (51.8% and 50.0% vs 64.4%, p &lt; 0.001 and p &lt; 0.001). We found no differences in cycle outcomes, implantation rate was 52,7%, 49,6% and 38,5% for 5, 6 and 7 Day respectively (P = 0,474). We speculate that this may be due to the small number of day 7 embryo transfers (n = 13), but we have 5 live births in our clinic after euploid Day7 embryo transfer.

Limitations, reasons for caution

Due to the decrease in the percentage of euploid embryos on day 7, such embryos should be transferred only after PGT-A. There is little information about the outcomes of Day 7 embryo transfers because they are the last embryos to be transferred.

Wider implications of the findings

Cultivation before day 7 should be introduced into routine practice as an option for patients over 35 years of age or with a known poor prognosis. Having previously assessed the laboratory’s capabilities and financial costs.

Trial registration number

not applicable