Maternal plasma phospholipid polyunsaturated fatty acids in early pregnancy and thyroid function throughout pregnancy: a longitudinal study

Background: Evidence has indicated that polyunsaturated fatty acids (PUFAs)-enriched diet could reduce inflammation because of thyroid autoimmunity in vivo, and therefore, enhance thyroid function. Objectives: We investigated whether early pregnancy plasma phospholipid PUFAs could benefit maternal thyroid function across pregnancy, which is critical to fetal brain development and growth in pregnancy. Methods: Within the National Institute of Child Health and Human Development Fetal Growth Studies–Singleton Cohort, we collected plasma samples longitudinally from 214 subjects [107 with gestational diabetes mellitus (GDM) matched with 107 controls] with a singleton pregnancy. We measured 11 PUFAs at early pregnancy (10–14 wk) and 5 thyroid biomarkers at 10–14, 15–26, 23–31, and 33–39 wk, including free thyroxine (fT4), free triiodothyronine (fT3), thyroid-stimulating hormone, antithyroid peroxidase, and antithyroglobulin. Associations of PUFAs with thyroid function biomarkers and relative risk (RR) of gestational hypothyroidism (GHT) during pregnancy were assessed using generalized linear mixed models and modified Poisson regression, respectively. Results: After sample weighting because of subjects with GDM over-representing in the analytic sample with biomarkers, eicosapentaenoic acid (EPA) at early pregnancy was associated with a reduction of 0.24 pmol/L (95% confidence intervals: −0.31, −0.16) in fT3 across gestation per standard deviation (SD) increment, whereas docosahexaenoic acid (DHA) at early pregnancy was associated with an increment of 0.04 ng/dL (0.02, 0.05) in fT4 across gestation per SD increment. Furthermore, EPA and docosatetraenoic acid (DTA) were associated with lower risks of persistent GHT (EPA—RR: 0.13; 0.06, 0.28; DTA—RR: 0.24; 0.13, 0.44) per SD increment. All significant associations remained robust in sensitivity analysis and multiple testing. Conclusions: Certain plasma phospholipid PUFAs were associated with optimal levels of thyroid biomarkers and even lower risk of GHT throughout pregnancy, which might be potentially targeted for maternal thyroid regulation in early pregnancy. Clinical Trial Registry: This trial was registered at https://beta.clinicaltrials.gov/study/NCT00912132?distance=50&term=NCT00912132&rank=1 as NCT00912132.