Females who are underweight or unexpectedly small at the time of their birth are more likely to have fertility problems later in life, a new study suggests.

Swedish scientists looked at over 1,200 women who were born from 1973 onwards, and who sought help for fertility problems between 2005 and 2010. All of the women were in heterosexual relationships when they sought help.

The scientists found that almost 40% of the cases of infertility were attributed to the women talking part, almost 27% were attributed to their male partners and the remaining cases were either unexplained or were due to a combination of problems with both the male and the female.

The study noted that women whose fertility problems were attributed to a female cause tended to be heavier than average. Being overweight or obese is already known to be a risk factor for infertility.

The study also noted that almost 4% of the women had been born prematurely, almost 4% were underweight at the time of their birth and almost 6% were unexpectedly small at that time.

When these results were analysed, the scientists found that women with fertility issues attributed to them were almost 2.5 times more likely to have been underweight at the time of their birth compared to those who had unexplained fertility issues or where the problems were attributed to the males.

The scientists also found that these women were almost three times more likely to have been unexpectedly small at the time of their birth.

The results stood even when other factors were taken into account such as current weight and previous births.

The scientists acknowledged that the number of women studied was relatively small and they all came from one geographical area, so it is unclear whether the results can be applied to all women.

However, they insisted that if the link between size and weight at birth and infertility is confirmed, this could have major implications for the future rate of fertility problems because medical advances mean that more and more small babies are now surviving into adulthood.

"As medical research and care advances, more infants will be born (with low birthweight or small size) and survive, which in turn might influence future needs of infertility treatment," the team from Linköping University said.

Details of these findings are published in the journal, BMJ Open.