Abstract
The present study reports on first-trimester reference ranges of plasma mineral Se/Zn/Cu concentration in relation to free thyroxine (FT4), thyrotropin (TSH) and thyroid peroxidase antibodies (TPO-Ab), assessed at 12 weeks' gestation in 2041 pregnant women, including 544 women not taking supplements containing Se/Zn/Cu. The reference range (2·5th-97·5th percentiles) in these 544 women was 0·72-1·25 µmol/l for Se, 17·15-35·98 µmol/l for Cu and 9·57-16·41 µmol/l for Zn. These women had significantly lower mean plasma Se concentration (0·94 (sd 0·12) µmol/l) than those (n 1479) taking Se/Zn/Cu supplements (1·03 (sd 0·14) µmol/l; P < 0·001), while the mean Cu (26·25 µmol/l) and Zn (12·55 µmol/l) concentrations were almost identical in these sub-groups. Women with hypothyroxinaemia (FT4 below reference range with normal TSH) had significantly lower plasma Zn concentrations than euthyroid women. After adjusting for covariates including supplement intake, plasma Se (negatively), Zn and Cu (positively) concentrations were significantly related to logFT4; Se and Cu (but not Zn) were positively and significantly related to logTSH. Women taking additional Se/Zn/Cu supplements were 1·46 (95 % CI 1·09, 2·04) times less likely to have elevated titres of TPO-Ab at 12 weeks of gestation. We conclude that first-trimester Se reference ranges are influenced by Se-supplement intake, while Cu and Zn ranges are not. Plasma mineral Se/Zn/Cu concentrations are associated with thyroid FT4 and TSH concentrations. Se/Zn/Cu supplement intake affects TPO-Ab status. Future research should focus on the impact of trace mineral status during gestation on thyroid function.
Highlights
Adequate maternal thyroid function during pregnancy is crucial for optimal fetal development, especially during the first 20 weeks when the fetal thyroid does not produce its own thyroid hormones (TH)(1)
Up to 9 % had an elevated titre of thyroid peroxidase antibodies (TPO-Ab) (>35 IU/l) and 10 % reported a history of thyroid dysfunction in the parents
The present study reports reference ranges (2·5th–97·5th percentiles), means and median concentrations of plasma mineral (Se, Zn and Cu) in an appropriately large sample of healthy pregnant women not taking supplements of these trace elements
Summary
Adequate maternal thyroid function during pregnancy is crucial for optimal fetal development, especially during the first 20 weeks when the fetal thyroid does not produce its own thyroid hormones (TH)(1). In a study from China, reference ranges for Cu. and Zn were established in different groups of women at a number of gestational ages and were compared with those of 552 non-pregnant matched controls[9]. Zn were established in different groups of women at a number of gestational ages and were compared with those of 552 non-pregnant matched controls[9] It was unclear whether the figures referred to plasma or serum concentrations and supplement intake was not recorded. A large sample size is needed in order to find subgroups of women not taking supplements containing these trace elements These sub-groups should preferentially share similar characteristics with the main group, enabling researchers to adapt the reference ranges to the general pregnant population
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