Boys born with lower-than-average weight are at higher risk of having fertility problems in later life, according to research.
Scientists have found that men who were born small for gestational age with birth weights in the bottom 10% had a 55% increased risk of infertility compared to those born in the normal weight range.
The findings did not show any link between gestational age and infertility in women.
The researchers from Denmark say that while the potential mechanisms for the link between birth weight and infertility in men are unclear, the mother’s health and lifestyle might play a role.
Ms Anne Thorsted, who carried out the study when she was part of a research group from the department of public health at Aarhus University, Denmark, said: “A suboptimal growth environment for the foetus, for whatever reason, could itself be detrimental to the development of sperm production and reproductive organs.
“It could also be speculated that the mother’s health and lifestyle during pregnancy could affect both foetal growth and the development of reproductive functions; for instance, we know already that if the mother smokes, this can have an impact on the foetus.
“Our results show that sometimes we must look at the very early life to find explanations of health problems that occur later in life.”
It is estimated that infertility affects one in seven couples in the UK, with around 30% of the cases attributed to male causing infertility.
Researchers looked at 5,594 men and 5,342 women in Denmark born between 1984 and 1987.
The team followed the test subjects through to adulthood until the end of 2017.
They found that 8.3% of the men born small for gestational age had been diagnosed or were being treated for infertility, compared to 5.7% of men born within the normal weight range.
Previous research has suggested a link between restricted growth of the foetus and an increased risk of penis and testicular problems in boys such as hypospadias, which is a malformation where the opening of the urethra is not at the tip of the penis, and cryptorchidism, a condition in which one or both of the testes fail to descend from the abdomen into the scrotum.
Ms Thorsted added: “It may well be that cryptorchidism, hypospadias and infertility have common origins in foetal life.”
But the researchers acknowledge that the participants, who were aged between 30 and 33 years by the end of 2017, still had a long reproductive life ahead and believe further analysis might be needed to see what the situation is in another 10 years’ time.
The findings are published in the journal Human Reproduction.