Scientists found that a plastic chemical sold as the safer replacement for phthalates showed up in over half of pregnant women and was linked to smaller babies

In 2002, a new plastic softener called DINCH went on sale as the answer to a growing health scare. Phthalates, the chemicals that make plastic soft and bendy, had been linked to premature birth and fertility problems, and manufacturers wanted something safer. Now researchers across the United States have checked the urine of thousands of pregnant women for traces of the replacement. Then they looked at the babies.

Across 6,617 pregnancies, higher levels of DINCH were linked to smaller newborns. Every tenfold increase in exposure went with a birth weight about 27 grams lower, roughly one ounce. Babies of the most exposed mothers were also more likely to be born small for their gestational age, below the 10th percentile for weight.

Exposure was common. Between 50% and 70% of the women had measurable traces of a DINCH breakdown product in their urine. For plastic chemicals in pregnancy, the replacement turned out to be one more exposure rather than a clean break.

“Our findings suggest that a chemical promoted as a safer replacement for phthalates and other plasticizers may affect how babies grow in the womb,” lead author Leonardo Trasande of NYU Langone Health said in a statement.

DINCH earned its safe reputation largely from animal testing. Regulatory studies in rats and rabbits found no harm to development even at high doses, while phthalates kept piling up evidence against them. In 2024, a study in The Lancet Planetary Health using the same American cohort linked phthalate exposure in pregnancy to preterm birth and estimated the cost to society in billions of dollars.

Human data on the replacement have been thin. A 2020 study of 420 babies conceived through a fertility clinic linked women’s DINCH levels before pregnancy to a higher chance of preterm birth. The new, much larger study did not find that link, which suggests the main effect, if real, may be on growth rather than timing.

The data come from the Environmental influences on Child Health Outcomes program, a US-wide project that follows families from pregnancy through childhood. Its participants come from a wide range of racial, ethnic and economic backgrounds, which the authors say makes the results more representative than past studies. Some women gave urine samples in more than one trimester, so this was the first study to track DINCH exposure across pregnancy.

Timing turned out to matter. Exposure in the third trimester was more strongly tied to lower birth weight for gestational age than exposure earlier on. Boys showed bigger differences in birth length, while girls were more likely to be small for their gestational age. Babies of Hispanic mothers and of mothers with less education were more affected, which the authors flag as a sign of unequal exposure.

“Even small differences in birth size can matter because fetal growth problems can raise the risk for heart disease, learning difficulties, obesity, and other issues that can echo into adolescence and adulthood,” Trasande said.

Animal and cell studies suggest a possible route. As DINCH breaks down, its by-products can interfere with hormones that guide fetal development and may trigger inflammation that affects how nutrients and oxygen reach the baby.

For an individual pregnancy, a one-ounce difference is small, and the authors suggest that families who are concerned can talk with their healthcare provider about ways to reduce exposure to plastic chemicals in pregnancy. Their bigger point is about regulation: Trasande argues that chemicals in food packaging and household products should be tested before they reach the market, not after problems appear. Pregnancy research is full of exposures that look worse than they are, as the debate over Tylenol in pregnancy showed, so independent confirmation will matter here too. It is also a reminder of how much pregnancy itself changes the body, down to the brain.

There are limits to what this shows. The study is observational, and the researchers caution that it cannot prove this plastic chemical causes smaller babies in pregnancy. Families with higher exposure may differ in diet, income or other chemical exposures that the analysis could not fully capture.

Urine levels change quickly, so even repeated samples give only snapshots of exposure. The effect per person is small, and the results apply to the United States. Trasande advises several groups that campaign on plastics and health, including the Food Packaging Forum Foundation, and represents the Endocrine Society at the UN plastics treaty talks. The study was funded by the National Institutes of Health.

Source

Trasande L, et al. “Prenatal exposure to di(isononyl) cyclohexane-1,2-dicarboxylate and adverse birth outcomes in the USA: a prospective analysis of births in a large American birth cohort.” Environment International, 2026.
DOI: 10.1016/j.envint.2026.110548

Also cited

Trasande L, Nelson ME, Alshawabkeh A, et al. “Prenatal phthalate exposure and adverse birth outcomes in the USA: a prospective analysis of births and estimates of attributable burden and costs.” The Lancet Planetary Health, 2024.
DOI: 10.1016/S2542-5196(23)00270-X

Zhang Y, Mustieles V, Yland J, et al. “Association of parental preconception exposure to phthalates and phthalate substitutes with preterm birth.” JAMA Network Open, 2020.
DOI: 10.1001/jamanetworkopen.2020.2159