A CHEMICAL used to make water bottles may cause premature births, a study suggests.

And experts warn the substance – Bisphenol A – could be affecting women before they even get pregnant.

Urine samples showed those with the highest levels of BPA before they conceived were six times more likely to have a premature birth.

BPA is used in the lining of some food cans, plastic containers and water bottles and disrupts hormones.

Experts already feared that exposing pregnant women to it increased the risk of premature birth.

It has also been linked to cancer and asthma.

Now docs at Harvard Chan School of Public Health in Boston have shown the impact on women could happen even earlier.

They took samples from 364 women before they fell pregnant. Of these, 32 gave birth to premature babies.

The research, which was presented at the annual meeting of the American Society for Reproductive Medicine in Denver, also found that phthalates, a chemical used in food containers, doubled the risk of early birth.

Jennifer Yland, who led the study, said: “Exposure to these chemicals is widespread, as they are found in food packaging, consumer products, medical devices, plastic bottles, and thermal receipts.”

It is thought that the two compounds can cause tiny changes to a woman’s eggs which later trigger premature labour.

Dr Peter Schlegel, president-elect of the American Society for Reproductive Medicine (ASRM), says: “This research points out that pre-conception factors are important but often poorly understood factors in reproduction.”