Association of mixed-exposure to phthalates during pregnancy with birth weight difference between twins

Objective To explore the association between mixed-exposure to phthalates (PAEs) during pregnancy and birth weight difference between twins.

Methods A prospective cohort study was conducted. From January 2013 to December 2016, 289 women with twin pregnancy from the Wuhan Twin Birth Cohort were recruited. The concentrations of eight PAEs metabolites in the urine of pregnant women in the first, second, and third trimesters were measured by high performance liquid chromatography-tandem mass spectrometry. These PAEs included monoethyl phthalate (MEP), monoisobutyl phthalate (MiBP), monobutyl phthalate (MBP), monobenzyl phthalate (MBzP), mono (2-ethylhexyl) phthalate (MEHP), mono (2-ethyl-5-oxohexyl) phthalate (MEOHP), mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono (2-ethyl-5-carboxypentyl) phthalate (MECPP). Multiple linear regression was used to analyze the relationships between mixed-exposure to these PAEs and weight difference between twins. Quantile g-computation and weighted quantile sum regression were used to evaluate the association between mixed-exposure to these PAEs and weight difference between twins.

Results The detection rates of all PAEs in urine were more than 80.00%. The highest detection rate was 97.00% for MBP, with a median concentration of 42.08 μg/L throughout the entire pregnancy. The lowest detection rate was 84.43% for MBzP, with a median concentration of 0.46 μg/L over the entire pregnancy. The median of birth weight difference between twins was 210 g.After adjustment for multiple confounders, multiple linear regression showed that the mixed-exposure to MEP, MBP, and MEHP throughout pregnancy was positively associated with the birth weight difference between twins. Weighted quantile sum regression results showed a positive correlation between mixed-exposure to PAEs and birth weight difference between twins during pregnancy. Moreover, quantile g-computation results showed that the birth weight difference between twins increased by 3.88% (95% CI: 0.25%-7.64%) with each quartile increase in the mixture of eight PAEs.

Conclusion The mixed-exposure to PAEs during the entire pregnancy could increase the birth weight difference between twins.