Background In euthyroid healthy adults thyroid function is known to be associated with obesity, insulin resistance, glycaemia, and dyslipidaemia. Little is known of similar associations in pregnancy, where maternal subclinical hypothyroidism or hypothyroxinaemia can have a detrimental effect on both mother and fetus.¹

Aims To assess the associations between reduced thyroid function (subclinical hypothyroidism/ hypothyroxinaemia), and maternal metabolic parameters in a non-diabetic Caucasian pregnant population.

Methods Detailed anthropometry and fasting biochemistry was obtained on 965 euthyroid Caucasian women with singleton, non-diabetic pregnancies recruited at 28 weeks gestation into the Exeter Family Study of Childhood Health (EFSOCH)² Thyroid function tests (TSH, FT4 and FT3) and TPO antibodies were measured. Trimester specific reference ranges were identified.⁽³⁾ We assessed the maternal metabolic parameters (BMI, FPG, triglycerides and insulin resistance (IR)) of those with and without mildly reduced thyroid function.

Results 82 women had hypothyroxinaemia (FT4 < 10.4 mmol/l (<10^th centile) and TSH < 3.0 mlU/l) and 133 women (13.9%) had subclinical hypothyroidism (TSH > 3.mlU/l). There was no difference in the metabolic parameters between those with and without subclinical hypothyroidism. Women with hypothyroxinaemia had higher BMI (29.8 (25.3–35.0) vs. 27.4(23.5–31.9), p < 0.001), FPG (4.5(0.4) vs 4.3 (0.4), p = 0.01), triglyceride (2.3 (1.7–3.2) vs 2.0 (1.4–2.8), p < 0.001) and IR (1.6 (0.9–2.7) vs. 1.3 (0.8–2.0), p = 0.001) than those without.

Conclusion Our study has identified that hypothyoxinaemia is associated with an altered metabolic profile. These findings may have implications for clinical care.

References

1. Breathnach FM, Donnelly J, Cooley SM, Geary M, Malone FD. Subclinical hypothyroidism as a risk factor for placental abruption: evidence from a low-risk primigravid population. Australian and New Zealand Journal of Obstetrics and Gynaecology. 2013 Dec;53(6):553–60

2. Knight B, Shields BM, and Hattersley AT. The Exeter Family Study of Childhood Health (EFSOCH): study protocol and methodology. Paediatric Perinatal Epidemiology 2006;20(2):172–9