Abstract
BackgroundThere is no clear cutoff value for thyroid‐stimulating hormone (TSH) level that defines subclinical hypothyroidism (SCH). Moreover, TSH levels can be affected by numerous factors. Although mild SCH has been implicated in miscarriage, the relationship between TSH levels and miscarriage remains unelucidated.MethodsWe reviewed nine known risk factors affecting TSH levels and 28 studies investigating the potential association between mild SCH and miscarriage, examining whether these factors were considered.Main findingsAmong 28 studies that examined whether mild SCH (TSH > 2.5 mIU/L) contributed to miscarriage, thyroid antibodies were measured in only 15. TSH measurement methods were described in 18 studies. Although the iodinated contrast medium used in hysterosalpingography (HSG) is stored in the body for a long time and is a risk factor for mild SCH, only one study described its potential impact on TSH levels. Nine studies, which concluded that mild SCH contributed to miscarriage, had thyroid status evaluated only after the onset of pregnancy, but not before.ConclusionTSH levels can be significantly affected by patient demographics and health history, country of origin, and fertility treatment. It is important to consider these factors while evaluating mild SCH. It remains unclear how mild SCH contributes to miscarriage.
Highlights
Overt hypothyroidism has been reported to increase the risk of miscarriage, premature birth, hypertensive disorders of pregnancy, placental abruption, postpartum hemorrhage, and Cesarean section.[1,2,3,4,5] Since overt thyroid dysfunction affects the mother and child, it must be adequately managed before and during pregnancy
In areas with a wide annual temperature range, it may be necessary to consider seasonal temperature variations, especially when evaluating for mild subclinical hypothyroidism (SCH). These results suggest that when thyroid-stimulating hormone (TSH) > 2.5 mIU/L is set as the universal cutoff value, there may be a difference in the prevalence of mild SCH in warm vs cold regions
This study evaluated mild SCH before ovarian stimulation, and TSH values in early pregnancy are unknown. These results suggest that the presence of mild SCH in early pregnancy may be a stronger contributor to miscarriage than the presence of mild SCH when planning pregnancy
Summary
Overt hypothyroidism has been reported to increase the risk of miscarriage, premature birth, hypertensive disorders of pregnancy, placental abruption, postpartum hemorrhage, and Cesarean section.[1,2,3,4,5] Since overt thyroid dysfunction affects the mother and child, it must be adequately managed before and during pregnancy. The results of the nationwide survey in the United States indicated that the basic value of TSH may differ depending on race.[38] This study found that African-American women had significantly lower TSH levels than Caucasian women (1.15 ± 0.02 vs 1.55 ± 0.03) and lower frequency of SCH (TSH > 4.5 mIU/L) (1.5% vs 6.6%). Elevated serum estradiol (E2) concentration due to ovarian stimulation with ART is known to affect the hypothalamic-pituitary-thyroid axis and might be a risk factor for SCH (high estrogen levels → rise in thyroxine-binding globulin (TBG) → transient decrease in FT4 → rise in TSH99).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
