Phthalate exposure during pregnancy associated with preterm birth

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1. Preterm delivery was associated with dose-dependent, higher urinary phthalate metabolites during pregnancy.

2. The magnitude of this association was greatest among spontaneous preterm deliveries.

Evidence Rating Level: 2 (Good)

Study Rundown: This study found that preterm birth was associated with higher urinary levels of four phthalate metabolites, a manmade chemical widely used in plastics. When stratified by type of preterm delivery, spontaneous deliveries (precipitated by preterm labor or premature rupture of membranes) had a greater magnitude of association compared with all preterm deliveries.

Phthalate levels were measured at multiple times during pregnancy, allowing for a better surrogate for overall pregnancy exposure. Additional strengths include large sample size that allowed for comparisons between types of preterm delivery. Limitations include lack of accounting for differences in diet as well as differences in metabolism and excretion of phthalates, both of which could confound the observed association. Future studies might assess pthalate exposure not only through urine but also through food diaries, or even by testing submitted food samples, and might also assess renal function to further characterize the observed associations.

Click to read the study in JAMA Pediatrics

Click to read an accompanying editorial in JAMA Pediatrics

Relevant Reading: Environmental Chemicals in Pregnant Women in the United States: NHANES 2003–2004

In-Depth [case-control study]: Researchers compared levels of nine urinary phthalate metabolites in pregnancy among 130 preterm (<37 wks gestation) deliveries and 352 randomly selected full-term control deliveries. In a subset of deliveries for which indication for preterm delivery was known (n=57), deliveries were stratified by type of delivery: spontaneous (i.e. spontaneous preterm labor or preterm premature rupture of membranes) or medically indicated preterm delivery (n=57).

Compared with controls, women who delivered preterm were more likely to have elevated urinary levels of 3 phthalate metabolites in pregnancy (MEHP: OR=1.35, p=0.01; MECPP: OR=1.40, p=0.002; DEHP: OR=1.33, p=0.02). The magnitude of these associations was greatest among spontaneous preterm deliveries. Relationship appeared dose-dependent when broken down into quartiles of urinary pthalate levels (MEHP P_trend=0.01; MECCP P_trend=0.003; DEHP P_trend=0.02).

By Maren Shapiro and Leah Hawkins, MD, MPH

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