P-681 Embryo utilisation rate and blastocyst formation rate correlate negatively with the oocyte yield and positively with live birth rate: an analysis from HFEA’s national database
Authors: Kulkarni A , Datta A , Campbell S , Nargund G 
Published: June 2023

Abstract

Study question
Do embryo utilisation rate (EUR) and blastocyst formation rate (BFR) correlate with oocyte yield and livebirth rate (LBR) in fresh IVF/ ICSI cycles?

Summary answer
EUR and BFR correlate positively with livebirth rate (LBR) but decline with increasing number of oocytes to a nadir when the fresh cycle LBRs plateaus.

What is known already
LBR in fresh IVF cycles plateaus once a certain number of oocytes are retrieved. While impaired endometrial receptivity with high ovarian response appears to be an underlying cause, other factors, such as decreasing competency of oocytes or embryos cannot be ruled out. Cytoplasmic dysmorphism of oocytes and chromosomal disorders have been shown to rise with increasing number of oocytes. Consequently, cumulative livebirth rate per oocytes has been reported to decline with increasing oocyte yield. When obvious male factor is excluded, the competency of oocytes can be reflected in the embryo grading.

Study design, size, duration
Retrospective analysis of 8015 fresh IVF/ ICSI cycles that met the inclusion criteria from the national database published by Human Fertilisation and Embryology Authority (HFEA) in the United Kingdom. We analysed 2 years of published data between January 2015 and December 2016.

Participants/materials, setting, methods
Population included couples at their first IVF treatment with single fresh blastocyst transfer, due to tubal or unexplained infertility among women aged &lt;40 years. Only cycles that produced at least 1 transferable blastocyst were included to determine the blastocyst formation rate. Inclusion criteria were designed to minimise other co-factors that may influence embryo quality. Linear regression analysis was done to find the correlation between EUR/ BFR and oocyte yield; multiple regression to predict livebirth

Main results and the role of chance
EUR (correlation coefficient = -0.156605, p &lt; 0.0001) and transferable BFR correlation coefficient = -0.156605, p &lt; 0.0001) declined with increasing number of oocytes. The findings were no different whether IVF or ICSI was performed.
Both EUR (OR 1.002, CI 1.001- 1,004) and (transferable) BFR (OR 1.005, CI 1.003-1.006) correlated positively with LBR (p &lt; 0.0001, for both), after adjusting for other confounders including age and method of insemination.
Both (transferable) BFR and EUR declined with the increasing number of oocytes falling to a nadir when around 8 oocytes were retrieved then remained static with higher oocyte yield. LBR in fresh cycles also reaches its peak at around 8 oocytes then plateaus.

Limitations, reasons for caution
Information on patient’s BMI or stimulation dose is not available in the HFEA database. However, it might have little impact in our findings given large sample size. Cycles with no blastocyst formation through extended culture were not included, as this intention to treat information was not available

Wider implications of the findings
Declining proportion of competent embryos may result in flattening of LBR graph in fresh cycles after certain number of oocytes retrieved. Increasing absolute number of competent embryos fails to boost fresh cycle LBR after a saturation point, We have to improve embryo selection than increasing ovarian stimulationto improve fresh LBR

Trial registration number
NA