AsianScientist (Aug. 6, 2019) – Despite a time limit imposed in many countries on the freeze-storage of sperm, a new study from China has found that the long-term cryopreservation of semen in a sperm bank does not affect future clinical outcomes. These findings have been published in Fertility and Sterility.
How long can sperm be kept frozen before it loses its ability to fertilize eggs? To answer this question, a team of researchers led by Dr. Huang Chuan of the Changsa-Hunan Sperm Bank, China, analyzed 119,558 semen samples from sperm donors and found that while sperm survival rate declines over time, freezing makes no statistical difference to the number of live births resulting from using frozen sperm.
For the purpose of the analysis, the samples were arranged in three groups: those kept in cryostorage for between six months and five years; those stored for between six and ten years; and those stored for between 11 and 15 years. The researchers first found that the frozen sperm’s survival rate after thawing did decline over the 15 year study period, from 85 percent to 74 percent 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 82.17 percent, 80.21 percent and 80.00 percent in the three storage groups respectively. Success rates were similarly comparable when the frozen sperm samples were used in in vitro fertilization, with live birth rates of 81.63 percent, 79.11 percent and 73.91 percent respectively.
The authors stressed that these very high success rates were achieved with screened donor sperm, which is not necessarily representative in quality of sperm from the general population.
“Donors at our sperm bank must be in good health according to physical examination and psychological evaluation,” said Huang, “and have no familial history of a genetic disease, so I think these live birth rates are appropriate.”
However, she added, the implications of the study remain, “that the long-term storage of sperm does not appear to affect live birth rates.”
There have been at least two reports in the medical literature on successful pregnancies using human semen stored for longer than 20 years, the first from the UK after 21 years storage, and the second from the US after 40 years storage.
However, many regulatory authorities set a time limit on sperm (and egg) storage of ten years, with longer exceptions for medical reasons such as for fertility preservation ahead of cancer treatment. But the literature offers no clear explanation for any these time limits.
Huang reports that the regulations governing China’s 26 sperm banks set no limit on the duration of semen storage, although the screening of sperm donors and semen is conducted strictly according to guidelines of the Chinese Ministry of Health for sperm quality (concentration, motility) and infection. All samples must be cryopreserved for a minimum six-month quarantine prior to rescreening for HIV, for example.
Nevertheless, because this study found a small but statistically significant decline in sperm survival rate over the 15-year study period, Huang and colleagues recommend that sperm banks should provide sperm in their order of cryopreservation.
The article can be found at: Huang et al. (2019) Long-term Cryostorage of Semen in a Human Sperm Bank Does Not Affect Clinical Outcomes.
Source: European Society of Human Reproduction and Embryology; Photo: Shutterstock.
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