Women with a history of miscarriage or subfertility are more likely to have subclinical hypothyroidism, finds a recent study conducted by researchers at the University of Birmingham, UK.
According to the study, the prevalence of subclinical hypothyroidism was about 20% in these women when using a thyroid-stimulating hormone (TSH) cutoff of 2.5 mIU/L. Subclinical hypothyroidism (SCH) or thyroid peroxidase antibodies (TPOAb) were found common in women with higher BMI or of Asian ethnicity, noted the authors.
SCH represents an early stage of thyroid dysfunction that can lead to preterm birth, miscarriage, subfertility, perinatal mortality, and pre-eclampsia. TPOAb also has been found associated with adverse pregnancy outcomes, and their presence increases the risk of subclinical and overt thyroid disease in pregnancy.
Levothyroxine (LT4) replacement is one of the recommended therapy for the treatment of pregnant women with SCH. However, it remained uncertain whether asymptomatic patients should be screened for mild SCH or TPOAb for initiating the treatment due to its possible suggestion of harm.
The study evaluated the factors associated with different thyroid dysfunction phenotypes in preconception asymptomatic women with a history of
miscarriage or subfertility.
The observational cohort study was conducted in 49 hospitals across the UK between 2011 and 2016. It involved women aged 16 to 41 years with a history of miscarriage or subfertility trying for a pregnancy. The main outcome measure was the rates of thyroid dysfunction.
Thyroid function and TPOAb data of 19,213 and 19,237 women, respectively were available for the study. The prevalence of abnormal thyroid function was found in 4.8%.
The study saw a higher prevalence of TPOAb among women with subfertility (10-31%) and recurrent pregnancy loss (17-33%) compared with the general population (6-20%)
However, around 8% of women in each group did go on to develop thyroid dysfunction and detection of this would not have been possible without knowing TPOAb status and performing the appropriate thyroid monitoring in pregnancy. Lowering the upper TSH to 2.50 mIU/L resulted in higher rates of SCH, 19.9%.
“The prevalence of undiagnosed overt thyroid disease is low. A TSH cutoff of 2.50 mIU/L to define SCH results in a significant proportion of women potentially requiring levothyroxine treatment,” wrote the authors.
The study, “The Prevalence of Thyroid Dysfunction and Autoimmunity in Women With History of Miscarriage or Subfertility,” is published in the Journal of Clinical Endocrinology & Metabolism.