Boys conceived using an assisted reproductive technique in which sperm is injected directly into the egg have lower fertility than average, scientists have found.
The results come from the first generation of boys conceived using a technique called intra-cytoplasmic sperm injection (ICSI), who are just reaching adulthood, and show that the young men have lower sperm quantity and quality than those conceived spontaneously.
ICSI is normally used to help couples conceive when the man has a low sperm count, or where there are abnormalities in the shape or movement of the sperm. The latest findings suggest that these problems tend to be passed on to the next generation - there is no suggestion that they are caused by the technique itself.
The study found that the men conceived through ICSI, who were aged between 18 to 22, had almost half the sperm concentration and half as many motile sperm (sperm that can swim well) than naturally-conceived men of a similar age.
ICSI men were nearly three times more likely to have sperm concentrations below the World Health Organisation’s threshold for “normal” fertility.
“These findings are not unexpected,” said Andre Van Steirteghem, emeritus professor at Vrije Universiteit Brussels, who led the work. “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.’”
The findings confirm for the first time that the problems that had caused the father’s infertility – usually genetic factors – appear to be inherited by their sons.
Scientists believe these genetic flaws would be passed on regardless of whether their children were conceived naturally or using ICSI.
“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,” said Van Steirteghem.
ICSI differs from conventional IVF treatments because the sperm is injected directly into the egg, rather than many sperm being mixed together with an egg and waiting for fertilisation to occur.
In 2014, the most recent year for which figures are available, around half of all IVF cycles in the UK involved ICSI, according to a report by the Human Fertility and Embryology Authority.
Nick Macklon, professor of obstetrics and gynaecology within medicine at the University of Southampton, said: “This was always going to be a concern, and couples were counselled that sons might inherit genetic flaws that nature was trying to get rid of by rendering the man infertile. It justifies our cautious approach. It isn’t any cause for alarm.”
Prof Richard Sharpe, an expert in male reproductive health at the University of Edinburgh, said: “In showing, as a group, that the ICSI sons have starkly abnormal semen quality compared with normal, non-ICSI-derived sons, the results suggest strongly that male fertility problems severe enough to require ICSI may be inheritable.
Importantly, the results are a reminder to us that Icsi is not a treatment for male infertility, but simply a way of bypassing a problem and leaving it for the next generation to deal with – something my generation seem horribly adept at doing.”
Prof Simon Fishel, managing director of Care Fertility, said that the findings were useful but not unexpected. “Just having low semen parameters is not evidence for the requirement of ICSI or IVF technologies,” he said. “We know many men with such are indeed able to conceive naturally. More follow up studies will be required to ascertain meaningful outcomes.”