Author Identifiers

Hamish Barblett

ORCID: 0000-0003-4513-8102

Date of Award


Degree Type


Degree Name

Master of Science (Human Biology)


School of Medical and Health Sciences

First Advisor

Associate Professor Peter Roberts

Second Advisor

Professor Phillip Matson


The increased cell numbers, presence of the blastocoel and rapid cell re-organisation have required the development of specific survival criteria post warm to effectively select the most viable blastocyst for transfer. Pre-freeze blastocyst expansion and post warm re-expansion have been shown to contribute significantly to the chances of an implantation and subsequent live birth. The aim of this study was to explore factors that influence the outcome of blastocyst transfers after vitrification and warming, and hopefully improve outcomes by further applying improvements in future cycles. Variables from 8 years of vitrified/warmed blastocysts were retrospectively compiled and analysed to determine the most significant contributors to outcome. There were 2466 transfers of either 1 or 2 vitrified/warmed blastocysts resulting in 796 (32.3%) clinical pregnancies and 751 (30.5%) live born babies. The patient/cycle specific variables of age: ≤38 years (OR: 2.01, 95% CI:1.48-2.73), transfer order: ≤ 2 (OR:1.32, 95% CI:1.10- 1.59) and cycle type: non-HRT (OR: 1.38, 95% CI:1.15-1.66) significantly influenced the live birth outcome. Blastocysts vitrified on day 5 of development had significantly improved outcomes to day 6 blastocysts (OR: 1.80, 95% CI: 1.37-2.35). A greater degree of blastocyst expansion on Day 5 further improved these outcomes (OR: 1.47, 95% CI:1.17-1.86). A grade 1 morphology rating significantly improved the outcomes of day 5 expanded blastocysts (OR: 1.51, 95% CI:1.24-1.85). The composition of the warming media and possibly the concentrations of osmotic buffer contributed to the survival of warmed blastocysts. Post warming assessment of the blastocyst showed that if the level of cell degeneration in the surviving and transferred embryo was less than 5%, this significantly influenced the outcome (OR:1.57, 95% CI:1.22-2.03). There was no significant difference if a blastocyst with ≥ 95% cell survival commenced re-expansion within 30 or 60 minutes after the warm (OR: 1.13, 95% CI:0.87-1.46). This study highlights the significance of even a small number of degenerative cells in the warmed blastocyst despite early commencement of re-expansion and warrants further prospective analysis.