A type of IVF treatment used by thousands of couples could lead to their sons suffering from fertility issues too, new research suggests.
Sons whose fathers had an intra-cytoplasmic sperm injection (ICSI) to conceive were found to have low sperm counts and poor-moving sperm.
Men born from ICSI were almost three times more likely to have sperm concentrations below 15 million per millilitre of semen, which is the World Health Organisation’s definition of normal.
Researchers said the findings “are not unexpected” as they had always suspected the problems that caused a man’s infertility - such as genetic factors - may be inherited by their sons.
During ICSI, a single sperm is injected directly into an egg. The treatment is often used to overcome issues such as low sperm count, abnormally-shaped sperm or sperm that is not moving well.
The treatment can also be used when sperm needs to be collected surgically from a man’s testicles or from a narrow tube inside the scrotum where sperm is stored.
If ICSI works and sperm successfully fertilises an egg, embryos are grown for up to six days in a laboratory and are then transferred to the womb.
In 2013, there were 37,566 embryos transferred using this type of treatment in the UK.
For the new study, published in the journal Human Reproduction, data was collected from 54 young men who had been born between 1992 and 1996, when ICSI first came about.
The results were compared with 57 men of a similar age conceived naturally.
Researchers from the Centre for Reproductive Medicine at the Vrije Universiteit Brussel (VUB) in Brussels found that a degree of “sub-fertility” had been passed on to the sons of fathers who were unable to conceive naturally, PA reported.
Blood and semen tests from the sons showed they had almost half the sperm concentration, and a two-fold lower total sperm count and total count of motile sperm, than men conceived naturally.
Professor Andre Van Steirteghem, from VUB and one of the co-authors of the study, said: “These findings are not unexpected.
“Before ICSI was carried out, prospective parents were informed that it may well be that their sons may have impaired sperm and semen like their fathers.
“For all the parents this information was not a reason to abstain from ICSI because, as they said, ‘If this happens, ICSI can then also be a solution for our sons’.
“These first results from the oldest group of ICSI-conceived adults worldwide indicate that a degree of ‘sub-fertility’ has, indeed, been passed on to sons of fathers who underwent ICSI because of impaired semen characteristics.”
Among sons who had lower sperm counts and less motile sperm, the results did not exactly match those of their fathers.
“The study shows that semen characteristics of ICSI fathers do not predict semen values in their sons,” added Steirteghem.
“It is well established that genetic factors play a role in male infertility, but many other factors may also interfere.”
Professor Adam Balen, chairman of the British Fertility Society, said he was “surprised” that some causes of infertility may be transmitted to children born by fertility treatments.
“While these young men may have lower sperm counts than the general population, they may still be able to father children without treatment and if they cannot they will have the opportunity to use the IVF/ICSI themselves,” he concluded.