REDUCING THE STRESS OF CULTURE? LOW LACTATE EMBRYO CULTURE MEDIUM INCREASES USABLE BLASTOCYST RATE FOR WOMEN OF ADVANCED MATERNAL AGE

to determine the impact of low-lactate concentration in continuous embryo culture media on useable blastocyst rates and clinical pregnancy rates. prospective validation of embryology and clinical outcomes for standard-lactate (Continuous Single Culture Complete; CSCM-C) compared to low-lactate continuous culture media (Continuous Single Culture-NX; CSCM-NX, Irvine Scientific). from 2019 to 2020, 1673 IVF or ICSI cycles had embryos cultured in either CSCM-C or CSCM-NX at a multicentre clinic (5 clinics) during a prospective culture media validation. CSCM-NX contains a lower concentration of lactate compared to traditional culture media (6-fold lower compared to CSCM-C) enabling direct assessment of whether a reduced concentration of the energy substrate lactate is biologically relevant in human embryos. Day 5 useable blastocyst rate (D5BUR), total useable blastocyst rate (TBUR) and clinical pregnancy rate (CPR) after first fresh or frozen transfer (primary outcome) were compared using two-tailed t-Tests or Pearson Chi-squared test. A p-value of <0.05 was statistically significant. low-lactate continuous media, CSCM-NX, resulted in a 7% increase in TBUR (52.8%) compared to CSCM-C (46.1%) for exclusively older patients (≥ 38 years; p=0.0186). Young patient (≤ 37 years) had a comparable TBUR for the two media (53.2% for CSCM-C and 53.6% for CSCM-NX). There was no difference in the D5BUR between CSCM-C and CSCM-NX according to female age group (40.9% and 41.9 % for ≤ 37 years; 32.4% and 37.3% for ≥ 38 years, respectively). Similarly, there was no difference in the primary outcome clinical pregnancy rate (44.4% and 47.6% for ≤ 37 years; 25.8% and 26.6% for ≥ 38 years, respectively). results from this large prospective media validation provide evidence that comparatively lower levels of lactate in continuous embryo culture media provide a beneficial metabolic environment for blastocyst development in older patients. The fact that the effect was confined to older patients may reflect higher levels of metabolic stress occurring within their embryos and therefore indicate lower lactate concentrations throughout culture improve metabolic conditions.