P–197 Two different strategies for embryo culture and selection: time-lapse with single-step medium and conventional incubator with sequential media. Are there differences in clinical results?
Authors: Alber. Rodriguez C , Valera M , Bori L , Meseguer F , Alegre L , Galán A , Meseguer M 
Published: August 2021

Abstract

Study question
Is there a significant difference in the clinical results of embryos cultured in time-lapse systems with single-step medium and conventional benchtop incubators with sequential media?

Summary answer
Embryos cultured in time-lapse systems and single-step media are more likely to achieve an ongoing pregnancy and have higher implantation rates than those cultured otherwise.

What is known already
One of the strategies for embryo culture in IVF consisted in conventional benchtop incubators combined with sequential culture media (CI-Seq). New generation time-lapse systems provide useful information on the morphokinetics of embryo development, but also a stable culture environment where embryos can develop undisturbed until blastocyst stage when paired with single-step culture media (TLS-SS). These features have the potential to improve embryo development and selection. Nonetheless, there is inconclusive evidence of whether this new culture strategy has a significant effect on clinical results of ICSI treatments. Studies on the matter are heterogeneous and reduced in both number and sample size.

Study design, size, duration
Unicentric retrospective cohort study. We compared the results of 11471 blastocyst transferences from 10276 ICSI treatments performed during 4 consecutive years, where embryos were cultured either on CI with sequential media (N = 5255) or a TLS with single-step medium (N = 5021). 3922 of the totals were fresh embryo transfers (ET) and 7549 frozen-thawed ET. We compared the implantation rate (IR) and ongoing pregnancy rate (OGPR) in both study groups, stratifying by ovum origin.

Participants/materials, setting, methods
Three models of TLS were used for embryo culture: EmbryoScope, EmbryoScope Plus (Vitrolife) and GERI (Genea Biomedx), as well as one CI (ASTEC). Sequential media: Cook, Origio, Vitrolife; Single-step media: Gems, Irvine, Life Global. Embryo scoring and selection was performed by ASEBIR criteria in the CI group, and by morphological and morphokinetic assessment for embryos cultured in TLS. Embryos were extracted from the CI only for media change. Statistical analysis: ANOVA tests and Logistic regressions.

Main results and the role of chance
A general Logistic Regression was performed, including egg origin, PGT-A and culture strategy to explain their impact in OGPR. Egg origin (OR = 1,094 (95%CI: 1,015–1,179); P = 0,019) and culture strategy (OR = 1,141 (95%CI: 1,060–1,229); P &lt; 0,001) were statistically significant, which confirms the need for stratification due to the heterogeneity of the groups. The total IR in the TLS-SS group was 54,68±48,84%, significantly higher than that of CI-Seq (49,18±47,91%; P &lt; 0,001). In ovum-donation treatments, a complete Logistic Regression for OGPR, with all typical confounding variables (age, BMI, nº oocytes, fresh/frozen transfer, number and day of ET) resulted in an OR = 1,187 (95%CI: 1,074–1,313; P = 0,001) favoring culture in TL-SS. IR in these treatments were 61,98±47,68% in TL-SS vs 55,08±46,58% in CI-Seq (P &lt; 0,001) in fresh transfers and 51,48±48,91% in TL-SS vs 44,39±47,67% in CI-Seq (P &lt; 0,001) in frozen-thawed ET. In autologous treatments with PGT a similar regression yielded an OR = 1,055 (95%CI: 0,889–1,252; P = 0,542) for culture strategy. The IR of genetically tested ET was not significantly different: 53,08±49,49% for TL-SS, 50,90±49,07% for CI-Seq, P = 0,246. In autologous procedures without PGT, culture strategy was not significant for OGPR (OR = 0,998 (95%CI: 0,835–1,191), P = 0,979) nor IR of fresh (49,75±48,91% TL-SS vs 44,23±47,36% CI-Seq; P = 0,081) nor frozen-thawed transferences (50,77±48,33% TL-SS vs 50,67±47,33% CI-Seq; P = 0,970).

Limitations, reasons for caution
After fertilization check, embryos were evaluated exclusively on D5/6. On D3, embryos cultured in CI were taken out only for a quick media change, but not for evaluation, and all handling was done in isolette cabins with controlled environmental conditions. Being a retrospective study, there is high variability in population.
Wider implications of the findings: A more homogenous prospective study, including comparison in life-birth rates, is necessary to extract final conclusions. However, our results suggest that the introduction of TLS and SS media in IVF laboratories might be a valid strategy to increase clinical results, especially in fresh embryo, thanks to an improved embryo selection.

Trial registration number
Not applicable