High concentrations of phthalates, chemicals found in a wide range of consumer products, in men may lead to delayed pregnancy for their female partners, a U.S. study said Wednesday.

Researchers at the National Institutes of Health and other institutions assessed the concentrations of phthalates in couples trying to achieve pregnancy.

Phthalates, sometimes called plasticizers, are used in the manufacture of plastics, to make them more flexible and are found in hundreds of products, such as fragrances, shampoos, nail polish, plastic film and sheets.

For the most part, people are exposed to phthalates by eating and drinking foods that have been in contact with containers and products containing the compounds.

The researchers studied 501 couples who were enrolled from the states of Michigan and Texas from 2005 to 2009, and were not being treated for infertility, but were trying to conceive a child.

The women taking part in the study ranged from 18 to 44 years of age, and the men were over 18. Couples provided urine samples that were analyzed for 14 phthalate compounds. Women kept journals to record their monthly menstrual cycles, intercourse and the results of home pregnancy tests. The couples were followed until pregnancy or for up to one year of trying.

They found that male urinary concentrations of the three metabolites of phthalates, monomethyl phthalate, mono-n-butyl phthalate, and monobenzyl phthalate, were associated with approximately a 20 percent increase in the time it took for the couples to achieve pregnancy.

Female urinary concentrations of these three metabolites were not associated with a delay in pregnancy.

"The delays in pregnancy we saw were comparable to those seen for cigarette smoking or with obesity," first author Germaine Buck Louis of the National Institutes of Health said in a statement.

The researchers said they examined only the time it took to achieve pregnancy and that further studies would be needed to determine if the compounds affected particular aspects of reproductive health, such as hormone levels.

Earlier studies had found that men with high concentrations of monomethyl phthalate had abnormalities in their semen and that men with high concentrations of mono-n-butyl phthalate had diminished sperm motility and reduced sperm count.

The study was published online in the journal Fertility and Sterility.