Risk factors of subclinical hypothyroidism and the potential contribution to miscarriage: A review

Abstract

Background There 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. Methods We 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 findings Among 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. Conclusion TSH 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.

Comparison of the safety between propylthiouracil and methimazole with hyperthyroidism in pregnancy: A systematic review and meta-analysis

“…well-established evidence that women with hyperthyroidism during pregnancy should be treated, as studies have shown that untreated hyperthyroidism may increase the risk of miscarriage [44]. Additionally, the risk of miscarriage has an association with the serum TSH level [45], suggesting that medical personnel should regularly monitor TSH levels in pregnant women to reduce the incidence of adverse pregnancy outcomes. It may be necessary to further study this issue to reveal whether ATDs treatment can improve other pregnancy outcomes of hyperthyroidism women [46].…”

Pregnancy outcomes and thyroid dysfunction: preterm birth risk assessment

“…Повышенная выработка ТТГ часто является ответом организма беременной на поздний гестационный возраст, ожирение, длительность климатического сезона с низкой температурой воздуха, стимуляцию яичников [9]. Дисфункцию щитовидной железы в период гестации также связывают с возникновением относительного дефицита йода, подавлением функции аденогипофиза и снижением уровня тиреотропина за счет усиленной секреции хорионического гонадотропина человека (ХГЧ), повышением уровня эстрогена, концентрации сывороточного тироид-связываю щего глобулина в сыворотке, дейодированием тироксина под влиянием плаценты [6,10].…”