Frozen sperm stored in liquid nitrogen at a sperm bank THOMAS FREDBERG/SCIENCE PHOTO LIBRARY

Long-term sperm freezing makes little difference to live birth rates. Despite a time limit imposed in many countries on storing frozen sperm, a large sperm bank study has found this may not be necessary.

The findings are based on a retrospective analysis of 119,558 semen samples from donors at the Hunan Sperm Bank in China.

The samples were arranged in three groups: those kept in cryostorage for between six months and five years, those stored for between six and 10 years, and those stored for between 11 and 15 years.


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The study found that the frozen sperm’s survival rate after thawing did decline over the 15-year study period – from 85 per cent to 74 per cent survival. However, this decline made little difference to the pregnancy and live birth rate in women using these samples for donor insemination, with cumulative live birth rates of 82.2 per cent, 80.2 per cent and 80.0 per cent in the three storage groups respectively.

Success rates were similarly comparable when the frozen sperm samples were used in IVF, with live birth rates of 81.6 per cent, 79.1 per cent and 73.9 per cent in the three groups.

Results of the study are being presented at the European Society of Human Reproduction and Embryology annual meeting in Vienna.