P-250 The exclusive role of sperm DNA fragmentation on the clinical outcome of a sibling donor oocyte cohort
Authors: Chung P , Kocur O , Xie P , Rosenwaks Z , Palermo G 
Published: June 2023

Abstract

Study question
Can sperm chromatin fragmentation (SCF) overwhelm the oocyte repair mechanism of healthy, young oocytes and impair embryo development and clinical outcome?

Summary answer
Elevated SCF, with its double-stranded DNA (dsDNA) component, remarkably impairs clinical outcome, despite oocyte repair mechanisms present in a sibling donor oocyte cohort.

What is known already
Despite a normal semen analysis, approximately 10-20% of males of reproductive age still have a subtle infertility. Therefore, conventional semen analysis is insufficient to identify the specific issues related to sperm function and its embryo developmental competence. Indeed, SCF with its dsDNA break component, is known to be associated with poor clinical outcome such as poor embryo development and pregnancy loss, by possibly increasing structural chromosomal abnormalities. Although a healthy oocyte may address certain levels of SCF, these oocyte repair mechanisms are incapable of repairing dsDNA breaks.

Study design, size, duration
Thirty-one couples were divided according to the degree and type of SCF, whether normal or abnormal, and shared the same sibling donor oocytes. The male partners in both groups had comparable semen parameters. Total SCF and dsDNA fragmentation were assessed in all men. Fertilization, implantation, clinical pregnancy (CPR; +FHB), delivery, and pregnancy loss rates were compared between the two cohorts.

Participants/materials, setting, methods
A total of 31 infertile couples underwent ICSI cycles utilizing split sibling donor oocytes due to advanced maternal age or premature ovarian insufficiency. Oocytes from the same donor were equally allocated among 2 couples.
Semen analyses were performed according to WHO 6th edition. Overall SCF was assessed by TUNEL with a ≤ 15% normal threshold. Double-strand DNA (dsDNA) fragmentation was assessed by neutral comet assay with ≤3% considered normal.

Main results and the role of chance
A total of 18 male partners (44.3 ± 7yrs) with a normal SCF of 8.9 ± 2% had their spermatozoa injected into sibling donor oocytes, while 13 male partners with abnormal SCF at 25.4% ± 11 (P&lt;0.001) had their spermatozoa injected into the remaining half. In the latter, the average dsDNA fragmentation rate was 3.6%, while in the former it was 0.3% (P&lt;0.001). Sibling donor oocytes injected with normal SCF resulted in a fertilization of 87.4% (146/167), implantation of 56.4% (22/39), +bHCG of 69.0% (20/29), CPR of 62.1% (18/29), and delivery rate of 51.7% (15/29). The other half of the sibling oocytes, injected with spermatozoa with elevated SCF, resulted in a fertilization of 70.8% (97/137) (P&lt;0.001), implantation of 15.4% (4/26) (P&lt;0.01), +bHCG of 42.1% (8/19), CPR of 21.1% (4/19) (P&lt;0.01), and delivery rate of 10.5% (2/19) (P&lt;0.01). The pregnancy loss in cycles utilizing the oocyte cohort injected with spermatozoa with normal SCF was 8.7% (2/23), while the pregnancy loss in those injected with spermatozoa with elevated SCF was 50.0% (2/4).

Limitations, reasons for caution
This preliminary study indicates that SCF and dsDNA fragmentation negatively affects clinical outcome, overwhelming oocyte repair mechanisms. Nonetheless, the study has a limited number of observations and needs to be validated in a larger cohort.

Wider implications of the findings
SCF, with its dsDNA fragmentation component, seems to contribute a higher incidence of chromosomal abnormalities. The compounded aneuploidy of male and female gametes may explain the compromised embryo development and higher pregnancy loss rate observed in infertile couples with apparently normal semen parameters and younger oocytes.

Trial registration number
not applicable