P-222 Early blastulation on day 4 predicts ongoing pregnancy in fresh transfer cycles
Authors: Gonzalez Marti B , Pessah C , Brami C , Tibi C , Sedbon E , Entezami F 
Published: June 2023

Study question

Do embryos with early blastulation (EB) on D4 show higher implantation potential compared to top D5 blastocysts in fresh elective single embryo transfer (eSET) cycles?

Summary answer

Fresh EB transfer with time start to blastulation (tSB)&lt;96.6h and time of expanded blastocyst (tEB)&lt;100h post-insemination is predictive of ongoing pregnancy for patients &lt;35.

What is known already

Expansion and hatching of blastocysts are correlated to implantation potential in fresh single transfers.

Thanks to time-lapse morphokinetics, several time-points can be analyzed during embryonic growth. Embryos with faster growing speed are correlated to euploid status. The tSB of &lt; 96.6h, day 4 post-insemination, is reported to have significant predictive value of euploid embryos, which are found to be associated not only with higher expansion scores, but also with shorter tSB, full expansion, and hatching. A study reported that significantly more embryos that reached the tSB by 100h implanted compared to those that did not.

Study design, size, duration

Prospective observational study in a single private hospital during 2022. In 160 cycles (n = 81 cIVF and n = 79 ICSI) an EB on D4 was observed. 48 patients (n = 28 ICSI and n = 20 cIVF) underwent a fresh eSET with an embryo showing EB on day 4.

Participants/materials, setting, methods

Patients with EB on D4 (tSB&lt;96.6h, tEB&lt;100h post-insemination) were enrolled regardless of indication, female age, attempt’s rank or technique. Those with a fresh eSET on D4 were included in this study.

Gardner’s classification was used to rate the blastocysts in Embryoscope + (Vitrolife). The outcome data of transfer for D4 blastocysts (B3/B4 AA-AB-BA) were compared to eSET with top D5 (B4/B5 AA) of reference group (female age ≤35).

The statistical analyses were performed by SPSS software.

Main results and the role of chance

In the study group, all the transferred embryos were graded according to Gardner’s classification as B3AA, or B3AB, or B3BA, or B4AA, or B4AB, or B4BA.

In the reference group, we chose only the fresh transfer cycles with ultra-top grade D5 embryos classified as B4AA or B5AA.

The results obtained in the overall population (n = 48) were compared to those obtained in the reference group (n = 92): age 34.0 ± 3.8 vs 31.8 ± 2.3, oocyte maturity (OM) 79.8% vs 80.3%, fertilization rate (FR) 80.0% vs 77.0%, overall blastulation rate (OBR) 78.1% vs 74.3%, top blastulation rate (TBR) 59.1% vs 54.4%, total pregnancy rate (PR) 75.5% vs 61.4%, implantation rate (IR) 58.3 vs 51.2% and ongoing pregnancy rate (OPR) 58.6% vs 47.1%, and showed a statistical difference only in PR (p&lt;0.05).

The results obtained in younger patients with age 32.1 ± 3.2 (n = 34) were also compared to reference group: OM 75.1% vs 80.3%, FR 85.0% vs 77.0%, OBR 78.1% vs 74.3%; TBR 58.7% vs 54.4% were comparable between the groups. A statistical difference was observed for PR (88.0% vs 61.4%, p&lt;0.01) IR (70.6% vs. 51.2%, p&lt;0.05) and OPR (70.6% vs 47.1%, p&lt;0.05).

Limitations, reasons for caution

The small size of the sample needs to be expanded in order to confirm the encouraging findings in a larger population, especially in older patients yielding more aneuploid embryos. The study will continue during 2023 and will compel the live birth rate.

Wider implications of the findings

When a D4 embryo with EB is available, the best option is the fresh transfer on D4. The increased implantation with EB seems to correlate with embryo euploidy and the advanced endometrial receptivity in stimulated cycles. Higher IR and OPR are reported even in patients with lower rate of aneuploidy.

Trial registration number

not applicable