This is the pilot phase of a randomised controlled trial.

The purpose of the pilot study is to assess the ability to recruit, randomise, adherence to the study protocol and plan for a full study.

The purpose of the full study will be to determine if a policy of embryo selection and transfer based on morphological evaluation and preimplantation genetic testing for aneuploidy (PGT-A) is a more clinically effective, safer, cost-effective and acceptable way to provide in vitro fertilisation (IVF) treatment in women of advanced reproductive age compared to the routine practice of embryo selection and transfer based on morphological evaluation alone.

The target population for the trial are women aged 35 - 42 years undergoing IVF±ICSI treatment.

Intervention The experimental strategy will be to perform PGT-A (also referred as preimplantation genetic screening - PGS) involving trophectoderm biopsy on embryos reaching the blastocyst stage on day 5/6/7 following egg collection. All embryos will be frozen after the biopsy procedure.

Comprehensive chromosome screening (CCS) of all chromosomes will be performed using next generation sequencing (NGS). Embryos will be categorised as euploid, mosaic euploid and aneuploid embryos and embryos will be ranked based on the degree of euploidy.

Only euploid embryos or mosaic euploid embryos deemed suitable to be replaced will be transferred in subsequent frozen-thawed embryo transfer cycles.

Comparison Women in the control arm will have the fresh embryo transfer procedure on day 5 following egg collection or a frozen-thawed embryo transfer as first line if clinically indicated in keeping with current routine practice. Embryo selection for transfer will be based on morphological criteria alone.

Inclusion Criteria:

• Inclusion criteria for the study would be women aged 35 - 42 years undergoing IVF ± ICSI for treatment of infertility
• Patients with 3 or more good quality embryos (assessed according to the embryo scoring system of the Association of Clinical Embryologists, UK) on day 3 following egg collection
• Ability to provide informed written consent

Exclusion Criteria:

• Women undergoing preimplantation genetic testing for inherited genetic disorders
• Gamete donation cycles
• Untreated hydrosalpinges
• Untreated uterine pathology (eg: endometrial polyps, submucous fibroids, intramural fibroids > 5 centimetres in maximum diameter, intrauterine adhesions, uterine septa)

If there was to be an individual participant data (IPD) meta-analysis on this topic or similar collaboration with other researchers in future, we will share IPD with other researchers.

The participants, care providers, investigators and outcome assessors will not be masked.