79. Associations of prenatal urinary phthalate exposure with preterm birth: the Maternal-Infant Research on Environmental Chemicals (MIREC) Study (lay summary)

Hu J, Arbuckle TE, Janssen P, Lanphear BP, Braun J, Platt RW, Chen A, Fraser WD, McCandless LC. Canadian Journal of Public Health. 2020 May 21. doi: 10.17269/s41997-020-00322-5

Preventing preterm birth is a public health priority. Infants who are born preterm (before 37 weeks) are at a higher risk of developing health complications.

Recent evidence suggests that phthalates may also play a role in preterm birth, but this evidence is not conclusive. Phthalates are man-made chemicals that are commonly added to plastics to enhance flexibility or stiffness in products such as food packaging, some medical devices and personal care products.  Just like the general population, pregnant women are exposed to phthalates on a regular basis in their day-to-day lives. When we are exposed to phthalates, our body changes them and creates new substances called metabolites so that they can more easily be excreted in urine.

Researchers used data from the MIREC study to investigate the potential role of phthalate metabolites on pre-term birth. These researchers collected urine samples from 1,857 women during the first trimester and measured 7 phthalate metabolites. They then looked to see whether these 7 metabolites were associated with pre-term birth or the timing of delivery. They also examined whether this was different for boys and girls.

The researchers showed that none of the 7 phthalate metabolites were associated with preterm birth or the timing of delivery. There was a small association between one metabolite and preterm birth among boys.

A limitation of this study was that only one urine sample was analysed for each pregnancy. Concentrations of phthalates are thought to fluctuate depending on when the urine sample is collected, and may even differ depending on when the sample is collected during pregnancy. Future studies should analyse more urine samples for each woman to better estimate her phthalate exposure during pregnancy.