Exposure to Bisphenol-A or BPA, which is used in certain plastics, may dramatically inhibit egg maturation and play a role in unexplained infertility, a new US study claims.

As many as 20 per cent of infertile couples in the US have unexplained reasons for their infertility, researchers said.

New research led by Catherine Racowsky, director of the Assisted Reproductive Technologies Laboratory at Brigham and Women's Hospital (BWH), shows that exposure to BPA (Bisphenol-A), a man-made carbon-based synthetic compound, could be a contributing factor as to why some infertile couples are having difficulty conceiving.

"To our knowledge, this is the first study that has shown that BPA has a direct effect on egg maturation in humans," said Racowsky.

"Because exposure to BPA is so ubiquitous, patients and medical professionals should be aware that BPA may cause a significant disruption to the fundamentals of the human reproductive process and may play a role in unexplained infertility," he said.

The randomised trial examined 352 eggs from 121 consenting patients at a fertility clinic. The eggs, which would have otherwise been discarded, were exposed to varying levels of BPA in a laboratory setting.

An egg from each patient was not exposed to BPA and served as the control.

Researchers then examined the eggs and found that exposure to BPA caused a decrease in the percentage of eggs that matured, increase in the percentage of eggs that degenerated and an increase in the percentage of eggs that underwent spontaneous activation, the abnormal process when an egg acts as though it has been fertilised, even though it has not been.

As the BPA dose increased, there was a decreased likelihood of maturity, an increased likelihood of degeneration and an increased likelihood of spontaneous activation.

Additionally, among the mature eggs, there was a significant trend toward a decreased incidence of bipolar spindles and aligned chromosomes with an increased dose of BPA.

"Our data show that BPA exposure can dramatically inhibit egg maturation and adds to a growing body of evidence about the impact of BPA on human health. I would encourage further research to gain a greater understanding of the role BPA plays in infertility," researchers said.

The study was published in the journal Human Reproduction.