The findings of a Swedish study of infertility indicate a link between a woman’s size and weight at birth and an increased risk for fertility difficulties once she’s of childbearing age. The exact cause-and-effect mechanism is still unknown but the study is considered important because babies born prematurely and those with low birth weight (LBW) or small for their gestational age (SGA) are surviving into adulthood in greater numbers than ever before. Knowing how the circumstances of their own births affect their fertility may help avert future woes and lead to better treatment options.

Cute baby on scaleThe study, led by Josefin Vikstrom, is the first to explore potential links between birth characteristics and infertility. It involved 1,293 women born in Sweden during or after 1973. As adults, each woman was involved in a heterosexual relationship and was undergoing infertility treatment from the Linkoping University Hospital’s Centre for Reproductive Medicine from 2005 through 2010.

The couples' infertility issues were attributed as:

  • 38.5% to the female
  • 27% to the male
  • 7% to both
  • 28% unexplained

As adults, most of the women in the study were of healthy weight but:

  • 25% were overweight
  • 5% were obese
  • 2.5% were underweight

At birth:

  • 4% of the women were premature
  • 5% were underweight
  • 6% were unexpectedly small

The women born at low birth weight were found to be 2.5 times more likely to have fertility issues as adults than those whose male partners were diagnosed as infertile or when infertility was unexplained. The women born unexpectedly small for gestational age (SGA) were three times more likely to be infertile than the women in the group where infertility was unexplained. These factors influenced female infertility even when the woman's current weight and history of previous childbirth were considered.

Furthermore, when infertility was attributed to a female factor, the adult women were more likely to be overweight or obese. The researchers note that excess weight is a well-documented factor associated with female infertility.

While the exact reason why the women's small size and weight at birth affects their reproductive health as adults remains elusive, the researchers speculate growth restriction during gestation might affect development of reproductive organs. In other studies, fetal growth restriction has been linked to reduced ovulation.

The research team acknowledges the limited scope of their study but expects its findings to be confirmed in similar studies involving more people. Also acknowledged is the limited geographic reach of the study. All study participants were born and raised in Sweden but similar studies done in other countries may produce different results.

Source: Vikstrom, Josefin, et al. "Birth characteristics in a clinical sample of women seeking infertility treatment: a case-control study." BMJ Open. BMJ Publishing Group Ltd. Mar 10, 2014. Web. Mar 19, 2014.