Association between maternal exposure to di(2-ethylhexyl) phthalate and reproductive hormone levels in fetal blood: the Hokkaido study on environment and children's health

Abstract

Prenatal di(2-ethylhexyl) phthalate (DEHP) exposure can produce reproductive toxicity in animal models. Only limited data exist from human studies on maternal DEHP exposure and its effects on infants. We aimed to examine the associations between DEHP exposure in utero and reproductive hormone levels in cord blood. Between 2002 and 2005, 514 pregnant women agreed to participate in the Hokkaido Study Sapporo Cohort. Maternal blood samples were taken from 23-35 weeks of gestation and the concentration of the primary metabolite of DEHP, mono(2-ethylhexyl) phthalate (MEHP), was measured. Concentrations of infant reproductive hormones including estradiol (E2), total testosterone (T), and progesterone (P4), inhibin B, insulin-like factor 3 (INSL3), steroid hormone binding globulin, follicle-stimulating hormone, and luteinizing hormone were measured from cord blood. Two hundred and two samples with both MEHP and hormones' data were included in statistical analysis. The participants completed a self-administered questionnaire regarding information on maternal characteristics. Gestational age, birth weight and infant sex were obtained from birth records. In an adjusted linear regression analysis fit to all study participants, maternal MEHP levels were found to be associated with reduced levels of T/E2, P4, and inhibin B. For the stratified analyses for sex, inverse associations between maternal MEHP levels T/E2, P4, inhibin B, and INSL3 were statistically significant for males only. In addition, the MEHP quartile model showed a significant p-value trend for P4, inhibin B, and INSL3 decrease in males. Since inhibin B and INSL3 are major secretory products of Sertoli and Leydig cell, respectively, the results of this study suggest that DEHP exposure in utero may have adverse effects on both Sertoli and Leydig cell development in males, which agrees with the results obtained from animal studies. Comprehensive studies investigating phthalates' exposure in humans, as well as their long-term effects on reproductive development are needed.

Figure 1. X-axis shows the MEHP quartiles, and Y-axis shows each hormone level.

The adjusted LSMs (95% confident intervals) of each hormone level in cord blood in relation to the MEHP concentration quartile fit to all study participants are shown with p-value for trend, and p for interaction, respectively, for (A) T/E2 (0.017, 0.846), (B) P4 (0.010, 0.520), and (C) inhibin B (0.004, 0.042). First quartile (≦5.90 ng/mL) is also compared to the 2nd (5.91–10.39 ng/mL), 3rd (10.40–15.30 ng/mL) and 4th (15.31+ ng/mL) quartile MEHP. Statistical significance of the P value was *p<0.017, **p<0.002 based on Bonferroni's correction. When compared to the LSM of the 1st MEHP quartile, the 4th MEHP quartile of T/E2, P4, and the 3rd and 4th inhibin B significantly decreased, whereas the 2nd MEHP quartile of T/E2 significantly increased. LSMs were adjusted for maternal age, smoking during pregnancy, alcohol consumption during pregnancy, gestational age, and the blood sampling week, infant sex, and interaction of sex and MEHP.

Figure 2. X-axis shows the MEHP quartiles, and Y-axis shows each hormone level.

In males, the adjusted LSMs (95% confident intervals) of each hormone levels in cord blood in relation to the MEHP concentration quartile (p-value for trend) are (A) T/E2 (0.357), (B) P4 (0.028), (C) inhibin B (<0.001), (D) INSL3 (0.005). First quartile (≦6.36 ng/mL) is also compared to the 2nd (6.37–10.25 ng/mL), 3rd (10.25–14.28 ng/mL) and 4th (14.29+ ng/mL) quartile MEHP. Statistical significance of the P value was *p<0.017, **p<0.002 based on Bonferroni's correction. LSMs were adjusted for maternal age, smoking during pregnancy, alcohol consumption during pregnancy, gestational age, and the blood sampling week.