The Prevalence of Thyroid Dysfunction and Autoimmunity in Women With History of Miscarriage or Subfertility
Rima Dhillon‐Smith, Aurelio Tobı́as, Paul Smith, Lee Middleton, Kirandeep K Sunner, Krystyna Baker, Samantha Farrell-Carver, Ruth Bender-Atik, Rina Agrawal, Kalsang Bhatia, Justin Chu, Edmond Edi‐Osagie, Ayman Ewies, Tarek Ghobara, Pratima Gupta, D. Jurkovic, Yacoub Khalaf, Khashia Mulbagal, Natalie Nunes, Caroline Overton, Siobhan Quenby, Raj Rai, Nick Raine‐Fenning, Lynne Robinson, Jackie Ross, Andrew Sizer, Rachel Small, Martyn Underwood, Mark D. Kilby, Jane Daniels, Shakila Thangaratinam, Shiao‐Yng Chan, Kristien Boelaert, Arri Coomarasamy
Abstract
OBJECTIVE: To describe the prevalence of and factors associated with different thyroid dysfunction phenotypes in women who are asymptomatic preconception. DESIGN: Observational cohort study. SETTING: A total of 49 hospitals across the United Kingdom between 2011 and 2016. PARTICIPANTS: Women aged 16 to 41years with history of miscarriage or subfertility trying for a pregnancy. METHODS: Prevalences and 95% confidence intervals (CIs) were estimated using the binomial exact method. Multivariate logistic regression analyses were conducted to identify risk factors for thyroid disease. INTERVENTION: None. MAIN OUTCOME MEASURE: Rates of thyroid dysfunction. RESULTS: Thyroid function and thyroid peroxidase antibody (TPOAb) data were available for 19213 and 19237 women, respectively. The prevalence of abnormal thyroid function was 4.8% (95% CI, 4.5-5.1); euthyroidism was defined as levels of thyroid-stimulating hormone (TSH) of 0.44 to 4.50 mIU/L and free thyroxine (fT4) of 10 to 21 pmol/L. Overt hypothyroidism (TSH > 4.50 mIU/L, fT4 < 10 pmol/L) was present in 0.2% of women (95% CI, 0.1-0.3) and overt hyperthyroidism (TSH < 0.44 mIU/L, fT4 > 21 pmol/L) was present in 0.3% (95% CI, 0.2-0.3). The prevalence of subclinical hypothyroidism (SCH) using an upper TSH concentration of 4.50 mIU/L was 2.4% (95% CI, 2.1-2.6). Lowering the upper TSH to 2.50 mIU/L resulted in higher rates of SCH, 19.9% (95% CI, 19.3-20.5). Multiple regression analyses showed increased odds of SCH (TSH > 4.50 mIU/L) with body mass index (BMI) ≥ 35.0 kg/m2 (adjusted odds ratio [aOR] 1.71; 95% CI, 1.13-2.57; P = 0.01) and Asian ethnicity (aOR 1.76; 95% CI, 1.31-2.37; P < 0.001), and increased odds of SCH (TSH ≥ 2.50 mIU/L) with subfertility (aOR 1.16; 95% CI, 1.04-1.29; P = 0.008). TPOAb positivity was prevalent in 9.5% of women (95% CI, 9.1-9.9). CONCLUSIONS: The prevalence of undiagnosed overt thyroid disease is low. SCH and TPOAb are common, particularly in women with higher BMI or of Asian ethnicity. A TSH cutoff of 2.50 mIU/L to define SCH results in a significant proportion of women potentially requiring levothyroxine treatment.