Those in the bottom 10 percent of birth weights had an 55 percent increased risk of infertility compared to those in the normal range. Picture: Needpix

London - Underweight baby boys face a higher risk of fertility problems later in life, a study suggests.

Those in the bottom 10 percent of birth weights had an 55 percent increased risk of infertility compared to those in the normal range. No such effect was found in women.

Researchers suggested the mother’s health could play a major factor. Anne Thorsted of Denmark’s Aarhus University said: "A suboptimal growth environment for the foetus, could itself be detrimental to the development of sperm production and reproductive organs.

"We know already that if the mother smokes, this can have an impact on the foetus... sometimes we must look at the very early life to find explanations of health problems that occur later."

Her team’s research, published in the journal Human Reproduction, examined 5 594 men and 5 342 women in Denmark born between 1984 and 1987.

The team tracked the participants through to adulthood, finding that 8.3 percent of the babies with the lowest weights for their gestational age went on to be diagnosed with or treated for infertility. For a baby born at 40 weeks, this meant a weight of less than 6lb 3oz (2.8kg).

By comparison, just 5.7 percent of men born within the normal weight range went on to encounter fertility problems. Once factors other than weight were taken into account – such as smoking – the increased risk was 55 percent.

The Aarhus team acknowledged that the participants are still in their early to mid-thirties, and that more analysis of fertility may be needed in ten years’ time.

Daily Mail