Jenni Laidman
November 18, 2013

Ubiquitous manmade chemicals known as phthalates, found in some plastics, personal care products, and foods, among other things, are associated with increased preterm births, especially those involving spontaneous preterm deliveries, according to a study published online November 18 in JAMA Pediatrics.

Kelly K. Ferguson, MPH, from the Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, and colleagues looked at 130 cases of preterm birth and 352 randomly assigned control participants and compared levels of phthalate metabolites averaged across 3 samples taken during pregnancy in an unrelated study. In a separate analysis, the researchers looked at phthalate levels for 57 cases of spontaneous preterm birth, defined as births preceded by spontaneous preterm labor or membrane rupture. Preterm births were any that occurred at fewer than 37 weeks’ gestation. Gestational age was validated by ultrasound during the first trimester. The births took place at Brigham and Women’s Hospital in Boston, Massachusetts. Most study participants were white, well-educated nonsmokers; few drank during pregnancy. Nearly half were nulliparous, and about 10% used assisted-reproductive technologies. Forty-four percent of the infants were boys.

Shanna H. Swan, PhD, professor, Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York City, author of an accompanying editorial, writes that the study made “an important public health contribution by demonstrating a sizable impact of phthalates, a class of commonly used chemicals, on a health outcome of major public health concern: the growing burden of preterm birth.”

The study authors found significant associations for the phthalate di-2-ethylhexyl phthalate (DEHP) metabolites and for metabolites of mono-n-butyl phthalate (MBP) among all preterm births and among spontaneous preterm births. The research identified additional associations for spontaneous preterm births with increased levels of mono-benzyl-butyl phthalate metabolites and MBP metabolites.

The odds ratio (OR) for all preterm births for the DEHP metabolite mono-(2-ethyl)-hexyl phthalate (MEHP) was 1.34 (95% confidence interval [CI], 1.07 – 1.68; P = .01); it was 1.65 (95% CI, 1.20 – 2.26; P =.002) for spontaneous preterm births. The OR for the DEHP metabolite mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) was 1.40 (95% CI, 1.13 – 1.74; P = .002) for all preterm births and 1.56 (95% CI, 1.15 – 2.13; P = .005) for spontaneous preterm births. For all DEHP metabolites, the summed OR was 1.33 (95% CI, 1.04 – 1.70; P = .02) for all preterm births and 1.63 (95% CI, 1.15 – 2.31; P = .006) for spontaneous preterm births.

Although the OR for several metabolites was not significant for preterm births in general, 4 were significant for spontaneous preterm births, including the DEHP metabolite mono-(2-ethyl-5-oxohexyl) phthalate (OR, 1.47; 95% CI, 1.04 – 2.08; P = .03) as well as mono-benzyl-butyl phthalate (OR, 1.41; 95% CI, 1.02 – 1.95; P = .04), mono-n-butyl phthalate (OR, 1.49; 95% CI, 1.08 – 2.06; P = .01), and mono-(3-carboxypropyl) phthalate (OR, 1.36; 95% CI, 1.01 – 1.81; P= .04).

Further, the research found that OR rose with the amount of phthalate metabolite found, with women in the 75th percentile for MEHP, MECPP, DEHP, and MBP at more than 2 times the risk for preterm birth as women in the lowest quartile. The effect was much stronger when only spontaneous preterm births were considered. For instance, women in the 75th percentile for MECPP had an OR of 5.23 for spontaneous preterm birth and an OR of 2.39 for any preterm birth. For MEHP, DEHP, and MBP, women in the highest quartile had ORs greater than 3.5 for spontaneous preterm births.

Dr. Swan suggests this stronger effect among spontaneous preterm births “makes it apparent that spontaneous deliveries are driving the effect estimates, and that the risk conveyed by phthalate exposure among the medically indicated deliveries is modest or negligible.”

The authors have disclosed no relevant financial relationships.

JAMA Pediatr. Published online November 18, 2013. Article extract