Objective: Restoration of euthyroidism with l-thyroxine reportedly reduces obstetric complications associated with subclinical hypothyroidism (SCH). The objective was to determine if obstetric outcomes of treated subjects were equivalent to euthyroid subjects.
Methods: This was a prospective cohort study. Subjects were considered euthyroid if serum thyroidstimulating hormone (TSH) was 0.4-3 mIU/L and free thyroxine (FT4) 10.29-17.05 pmol/L with negative thyroid peroxidase antibodies (TPOAb). Subclinical hypothyroidism was diagnosed if FT4 was 10.29-24.45 pmol/L and TSH 2.5-3 mU/L with positive TPOAb, or TSH > 3.0 mU/L regardless of antibody status. Subclinical hypothyroidism subjects were treated with l-thyroxine until TSH < 2.5 mIU/L. Data were analysed with Stata (StataCorp, USA).
Results: Seven hundred and sixty-nine singleton pregnancies were screened; 96% at 14 weeks gestation. Five hundred and eleven (66%) were euthyroid by study definition. Prevalence of SCH was 1.9% (15/769); 26% (4/15) were TPOAb positive. Eighty-one per cent were treated according to protocol; compliance was 54%. Mean gestational age (GA) at first endocrinologist visit was 22.7 ± 2.7 weeks. Normal TSH was documented in 36% at GA 33 ± 2.94 weeks. Subjects with SCH had significantly greater pre-existing history of preterm premature rupture of membranes (PPROM) and preterm labour, Caesarean sections for non-reassuring fetal heart rate and neonatal necrotizing enterocolitis.
Conclusion: L-thyroxine appeared to reduce obstetric complications. However, prevalence of SCH was low and compliance was < 50%.
Keywords: Hypothyroidism; obstetric outcomes; subclinical.