Sperm epigenetics linked to likelihood of pregnancy

A new method for determining the 'biological age' of sperm may be a useful predictor of pregnancy success.

A study conducted at Wayne State University School of Medicine, Detroit, Michigan, and published in the journal Human Reproduction, found a 17 percent decrease in reproductive success after twelve months of trying to conceive for couples with a male partner with biologically 'older' sperm. This method was based on levels of methylation in sperm which are known to accumulate with age, known as an 'epigenetic clock'.

'Chronological age is a significant determinant of reproductive capacity and success among couples attempting pregnancy, but chronological age does not encapsulate the cumulative genetic and [environmental …] factors' said Dr Richard Pilsner, the lead author of the study. '[An epigenetic clock] serves as a proxy measure of the "true" biological age of cells.'

The study included 379 US couples from the Longitudinal Investigation of Fertility and Environment Study, where DNA methylation analysis was conducted on the sperm of the male partner. Partners had not undergone fertility treatment previously but had been off contraception with the intention of becoming pregnant. The study findings were also validated in an independent IVF cohort.

While the chronological and epigenetic ages were strongly correlated, the study reiterated that the latter would capture various features which drive methylation and may enhance pregnancy success prediction. For example, smokers, on average, showed higher sperm epigenetic ages, demonstrating the additional information provided by this measure.

The authors argue that a sperm epigenetic clock may be useful as a future biomarker of reproductive success, and that the study specifically highlights the importance of the male partner in determining this. Additionally, it is hoped that this tool might inform decisions surrounding potential infertility treatment at early stages.

'Semen quality outcomes utilising World Health Organisation guidelines have been used to assess male infertility for decades, but they remain poor predictors of reproductive outcomes', said Dr Pilsner. 'The ability to capture the biological age of sperm may provide a novel platform to better assess the male contribution to reproductive success, especially among infertile couples.'