Abstract Study question Does the intraovarian injection of autologous platelet rich plasma (A-PRP) improve the outcomes of subsequent in vitro fertilisation (IVF) treatments. Summary answer Intraovarian injection of A-PRP improves embryological performance and pregnancy outcomes in subsequent IVF treatments, but the beneficial effects may be lost with time. What is known already A-PRP has been widely used in other medical fields to optimise treatment outcomes. In IVF, emerging evidence has shown its potential benefit in promoting endometrial quality via release of a range of growth factors and cytokines. More recently it has been proposed that intraovarian injection of A-PRP may have the potential to “activate” some resting follicles in a selected group of patients. In this registered clinical trial, we aimed to evaluate embryology performance and pregnancy outcomes following ovarian injection of A-PRP in patients with poor ovarian function or premature ovarian failure. Study design, size, duration This is a registered (ID= ACTRN126190012061128) prospective clinical trial with recruitment commencing in November 2019. All participating women undergoing A-PRP treatment due to poor ovarian function or premature ovarian failure were reviewed for eligibility for this study. Inclusion criteria were restricted to women who had completed at least one IVF cycle before and after A-PRP injection as of January 2022. Participants/materials, setting, methods All A-PRP treatments were prepared using a commercial kit (Alocuro) approved by the Australian Therapeutic Goods Agency. Up to 3 subsequent IVF cycles post A-PRP injection were included for analysis. Embryological parameters included numbers of follicles, oocytes and embryos yielded per cycle. Paired comparisons were performed between cycles of the same patients before and after A-PRP injection. Cumulative ongoing pregnancy outcomes were also evaluated up to 3 IVF cycles post A-PRP injection. Main results and the role of chance 36 women were included in the analysis, average age 41.14±3.56 years with 4.61±2.91 unsuccessful previous IVF attempts at the time of A-PRP injection. Their serum FSH was reduced from 13.04±8.97 mIU/mL before A-PRP injection to 11.06±.56 mIU/mL post injection. In reference to the IVF cycle immediately before A-PRP injection, an improving trend in the embryology parameters was identified in the subsequent 1st, 2nd, and 3rd IVF cycles; as demonstrated in the numbers of follicles (2.39±1.76, 2.86±2.06, 2.52±1.65 and 2.46±1.66), oocytes (1.86±1.48, 2.56±2.08, 2.43±1.90 and 2.08±1.93) and embryos (1.30±1.03, 1.45±1.39, 1.80±1.67 and 1.20±1.48). Although the comparisons above did not reach statistical significance, the rise in oocyte numbers in the 1st IVF cycle was close to statistical significance (P = 0.08). It should also be noted that the highest improvement in follicle and oocyte numbers was seen in the 1st IVF cycle after A-PRP injection, while embryo number peaked at the 2nd IVF cycle. Three out of 36 women (P = 0.08) achieved ongoing pregnancies after the 1st round IVF cycles with inclusion of associated frozen embryo transfers as applicable. After the 2nd round, 4 out of the 36 women (P = 0.04) achieved ongoing pregnancy but no additional pregnancies from the 3rd round. Limitations, reasons for caution Comparisons performed in this study were not randomised, with the patients themselves used as their own controls. Therefore cycle associated variations may not be eliminated. Sample size was relatively small, and findings were restricted to a selected patient group. Wider implications of the findings Ovarian injection of A-PRP seems to improve both embryology performance and cumulative pregnancy outcomes. However the beneficial effect post injection seems to fade with time. A further randomised study is warranted to specify the timeframe of this diminishing effect in order to better guide clinical practice. Trial registration number ACTRN126190012061128