Infertility risk higher for men born underweight, finds study
Men have a higher risk of infertility if they are born small for their gestational age, research suggests.
A study in Human Reproduction found that being born below average size was associated with infertility in adulthood among men, but no association was found for women.
Researchers from Denmark examined birth records of 5,594 men and 5,342 women born between 1984 and 1987. They compared this with infertility data held on Danish health registers from the participants’ eighteenth birthday until the end of 2017.
In the cohort just over 10% of men and women were born small for their gestational age.
The odds of infertility as an adult were 55% worse for men born below weight than those born at an average weight, even when taking into account factors such as mother’s age, maternal smoking and mother’s pre-pregnancy weight.
The research found that 8.3% of boys born underweight experienced infertility as adults compared with 5.7% of those born at an average weight. This may be due to two genital malformations, hypospadias and cryptorchidism, the study concluded.
Hypospadias is a congenital condition in which the opening of the urethra is on the underside of the penis instead of at the tip, whilst cryptorchidism is the failure of one or both of the testes to descend from the abdomen into the scrotum.
It is estimated that one in seven heterosexual couples in the UK experience infertility. Reproductive health problems are equally split between men and women, with both accounting for a third of known causes. The remaining third is due to unclear causes.
Anne Thorsted, co-author of the research from Aarhus University in Denmark, said: ‘Our results show that sometimes we must look at the very early life to find explanations of health problems that occur later in life.'