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Even before pregnancy, exposure to a certain family of endocrine-disrupting chemicals was tied to shorter gestation, researchers reported.

In an analysis of 420 singleton births, higher maternal concentrations of several phthalate metabolites -- commonly found in plastics -- prior to conception was associated with a higher risk for preterm birth, according to Carmen Messerlian, PhD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues.

Even after adjustment for known risk factors tied to preterm birth, such as the use of assisted productive technology, a higher total concentration of several metabolites belonging to the common di(2-ethylhexyl) phthalate (DEHP) family was linked to a 50% higher risk for birth before 37 completed weeks' gestation (risk ratio 1.50, 95% CI 1.09-2.06, P=0.01), they stated in .

Out of the seven separate DEHP metabolites included, the four that were independently tied to preterm birth were MEHP, MEHHP, MEOHP, and MECPP. DEHP chemicals are often found in plastic household items such as shower curtains, garden hoses, rain gear, and swimming pool liners. This compound is also commonly used in certain medical devices, including IV catheters, tubing, and bags.

The authors found that the increased preterm birth risk still remained significantly higher after adjustments for maternal prenatal biomarker exposure (RR 1.69, 95% CI 1.17-2.44, P=0.006).

They also reported that the association between prenatal DEHP exposure and preterm birth was significant for male infants (RR 2.01, 95% CI 1.17-3.45), but not female infants (RR 1.22, 95% CI 0.79-1.88).

In an , Ruth A. Etzel, MD, PhD, of the George Washington University in Washington, called the findings "novel," pointing out that the study indicated that mothers trying to lower their risk for preterm birth by limiting environmental chemical exposure during the first trimester of pregnancy "may be too late."

Etzel added that the World Health Organization, among other scientific organizations, has suggested public health efforts put focus on maternal health even prior to the conception, such as recommending that women of childbearing age to reduce environmental chemical exposure.

"Many reproductive toxicants are present in air, water, food, and products in the home; it is difficult to prescribe specific actions that predictably eliminate these ubiquitous chemicals," she explained, adding that "upstream actions" through policy changes to reduce these environmental toxins should be strongly considered.

The authors looked at singleton births from subfertile couples at an academic fertility center in Boston born from 2005 to 2018. Both female and male partners provided one urine sample each prior to conception, used to measure phthalate metabolite exposure. Couples then provided more urine samples during fertility procedure, and females provided more urine samples for analysis at weeks 6, 21, and 35 weeks' gestation.

Of the 420 singleton births, only 34 infants (8%) were born preterm, which was a study limitation.

The researchers suggested that future studies parse out the relationship between preconception phthalate exposure to certain subtypes of preterm birth, including preterm premature rupture of membranes, indicated preterm birth, and spontaneous preterm labor.

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