Exposure to the chemical bisphenol A (BPA) may reduce fertility among women who already have fertility problems, a new study suggests.
The study involved women trying to conceive children through in vitro fertilization (IVF), a fertility treatment that includes taking hormones to stimulate egg production. These eggs are then collected, and researchers attempt to fertilize them in a laboratory.
In the study, doctors collected 24 percent fewer eggs from women with high levels of BPA in their bodies, compared with women who had low levels of the industrial chemical.
Women with high BPA levels also had fewer eggs that were successfully fertilized.
BPA is found in many products, including canned foods, plastics, dental sealants and credit card receipts. The chemical does not stay in the body for a long time, so a person's BPA levels can vary substantially depending on his or her exposure in a given day.
The new findings agree with animal studies suggesting that BPA exposure reduces fertility. For example, a study published last month found BPA exposure increased the risk of abnormal egg development in monkeys.
The new study found only an association, not a direct cause-effect link. In addition, the researchers did not look at how many women became pregnant, so they can't say whether BPA affects pregnancy rates, said Dr. Avner Hershlag, chief of the Center for Human Reproduction at North Shore University Hospital in Manhasset, N.Y., who was not involved in the study.
However, if the results are confirmed by future research, doctors could one day measure BPA levels in women who fail to become pregnant through IVF, or who have low egg yields during the process, Hershlag said. Doctors could look at whether reducing BPA exposure in women with high levels makes a difference, he said.
In the new study, Dr. Russ Hauser, of Harvard School of Public Health, and colleagues analyzed information from 174 women who underwent IVF between 2004 and 2010. The researchers measured BPA levels in two urine samples from the women: one taken during hormone treatment and one taken two weeks later, on the day the eggs were collected. Nearly 90 percent of participants had BPA in their urine.
On average, about 12 eggs were collected from women with the lowest BPA levels, whereas nine eggs were collected from women with the highest BPA levels.
Upon trying to fertilize the eggs, the researchers found that women with high BPA levels had 27 percent fewer eggs that could be fertilized than women with low BPA levels.
It's not clear whether BPA might affect egg production in women in the general population — it's possible that women undergoing IVF are particularly susceptible to the effects of the chemical, the researchers said.
Studies in which samples are collected every day of the IVF cycle could better determine the effects of BPA exposure, the researchers said.
The study was published online Sept. 26 in the journal Human Reproduction.