Table 6.
Estimates of maternal FT3 serum concentration for the 10th, 50th and 90th percentile of maternal serum compound concentration.
| Independent variable | Maternal FT3 serum concentration (pmol/l) for the | ||
|---|---|---|---|
| 10th compound percentile | 50th compound percentile | 90th compound percentile | |
| DDEa | 4.361 | 4.240 | 4.033 |
| PCB 74 | 4.283 | 4.260 | 4.144 |
| PCB 99 | 4.286 | 4.242 | 4.156 |
| PCB 118 | 4.328 | 4.251 | 4.10 |
| PCB 138 | 4.353 | 4.251 | 4.069 |
| PCB 153 | 4.349 | 4.249 | 4.066 |
| PCB 156 | 4.307 | 4.239 | 4.098 |
| PCB 170 | 4.311 | 4.241 | 4.102 |
| PCB 180a | 4.374 | 4.227 | 4.021 |
| PCB 183 | 4.370 | 4.257 | 4.046 |
| PCB 187 | 4.353 | 4.258 | 4.053 |
| PCB Group 1b | 4.355 | 4.251 | 4.071 |
| PCB Group 2c | 4.340 | 4.251 | 4.075 |
Robust linear regression models with the maternal FT3 serum concentration as a dependent variable and the respective compound of interest as independent variables reveal lower FT3 concentrations for higher compound concentrations. Analyses were adjusted for maternal age, maternal BMI and maternal serum lipid concentration.
The underlying model reached the level of significance for all compounds and both PCB groups, except PCB 156.
PCB polychlorinated biphenyl, DDE dichlorodiphenyldichloroethylene, FT3 free triiodothyronine (pmol/l).
aFor DDE and PCB 180, a polynomial of second order with FT3 serum concentration as a dependent variable reveals significant higher FT3 serum concentrations for women with higher compound serum concentrations. We checked if a term of higher order was necessary by modelling the associations with polynomial and compare them to the linear model using analysis of variance. If the higher-order term resulted in a significant model improvement, the results were changed accordingly. Otherwise, the previous result was kept.
bGroup 1: sum of potentially antiestrogenic and dioxin-like PCB congeners (74 + 118 + 138 + 156 + 170).
cGroup 2: sum of phenobarbital, CYP1A and CYP2B inducing PCB congeners (99 + 153 + 180 + 183).