Relationship of urinary concentrations of 9 phthalate metabolites with serum thyroid hormones in pregnant women and their newborns in Taiwan

Abstract

Background: A growing number of animal and epidemiological studies have indicated that environmental chemicals can interrupt the regulation of thyroid function. However, only a few studies were reported the effects of phthalates exposure on thyroid function in pregnant women and their newborns. Objective:The present study was to investigate the association between maternal phthalate exposures and their thyroid hormones, and cord thyroid hormones in their newborns from the general population in Taiwan. Methods: A total of 150 maternal and infant pair was recruited from E-Da hospital in the southwestern Taiwan, from 2009 to 2010. Pregnant women were interviewed by a standardized questionnaire, and we also collected their urine and blood samples at third trimester and cord blood samples at delivery. Nine phthalate metabolites (MEHP, 5OH-MEHP, 5oxo-MEHP, MiBP, MnBP, MBzP, MEP, MMP, and MiNP) in urine samples were determined by liquid chromatography/ electrospray tandem mass spectrometry (LC-ESI-MS/MS). Serum thyroid hormones of pregnant women and cord thyroid hormones (TSH, Free T4, T3 and T4) of newborns were measured by enzyme immunoassay (EIA). Results: Mean (±SD) age and pre-pregnant BMI of pregnant women were 29.4±4.9 years old and 22.0±3.5, respectively. Less than 3% of them had smoking and drinking habit. Mean gestational age of newborns were 38.5±1.1 weeks. For the maternal urinary phthalate metabolites, the three most higher concentration were MnBP (median, 37.81 mg/g Cr), MEP (34.51 mg/g Cr) and 5OH-MEHP (21.73 mg/g Cr). Significant negative correlation were found between TSH levels in cord serum and maternal urinary 5oxo-MEHP (r=-0.221, p<0.01), 5OH-MEHP (r=-0.263, p<0.01) and MBzP (r=-0.263, p<0.01). After adjusted for age, pre-pregnant BMI, gestational age, maternal TSH and other phthalate metabolites, maternal urinary MBzP and MEP concentrations showed a negative association with TSH levels in cord serum (?=-3.04, p=0.003 for MBzP; ?=-2.01, p=0.046 for MEP). Conclusion: Maternal exposure to butyl benzyl phthalate (BBP) and diethyl phthalate (DEP) may affect thyroid activity of their newborns, however, how BBP and DEP affects newborns’ thyroid function is unclear. Further studies are need to elucidate this mechanism and to investigate whether any other factors related to BBP and DEP exposure alter the newborns thyroid function.