Variation in treatment practices for subclinical hypothyroidism in pregnancy: US national assessment

Update on therapeutic use of levothyroxine for the management of hypothyroidism during pregnancy

Hypothyroidism is a relatively common finding during pregnancy. This may be due either to the presence of existing thyroid disease and/or to the increased demands that pregnancy places the thyroid gland to provide thyroid hormones for the mother and the developing fetus. There is no doubt that overt hypothyroidism is associated strongly with adverse pregnancy outcomes, including miscarriage. Meta-analyses show that thyroid hormone replacement with levothyroxine (LT4) reduces the risk of adverse pregnancy outcomes in the setting of overt hypothyroidism. Accordingly, management guidelines in this area are unanimous in recommending intervention with to control the level of thyrotropin (TSH) to below 2.5 μIU/mL. The evidence for an adverse impact of subclinical hypothyroidism (SCH) on pregnancy outcomes is less clear, although meta-analyses suggest that SCH reduces the chance of a successful pregnancy outcome. Guidelines also support intervention for some patients with SCH, particularly where TSH is high (>10 μIU/mL), or where TSH is above its trimester-specific reference range in a woman with thyroid autoimmunity (giving LT4 to euthyroid women with thyroid autoimmunity is not supported). Real-world evidence suggests that hypothyroidism in pregnancy is often overlooked or that LT4 is not given appropriately to gain tight control of TSH. More research is needed to identify the barriers to optimal thyroid care with LT4 at this crucial time.

Maternal thyroid function in multiple pregnancies - a systematic review

BACKGROUND

The function of the thyroid gland during pregnancy undergoes physiological changes to ensure the proper amount of thyroid hormones for both the pregnant woman and the fetus. Multiple pregnancies (MP) are characterized by specific differences compared to single pregnancies, e.g., higher concentrations of human chorionic gonadotropin, which also affect thyroid function. The aim was to collect available knowledge on maternal thyroid function in MP.

METHODS

We have systematically searched three databases: the PubMed/MEDLINE, Scopus and the Cochrane Library. The last search was run on the 4th of August 2022. We included full-text original observational and experimental studies written in English. Case reports, editorials, letters, conference abstracts, reviews and meta-analyses were excluded. No time criterion was established. Studies were considered eligible if at least one maternal thyroid function test was performed and reported. Studies on MP with a co-existing mole were excluded. The risk of bias was assessed with the use of the AXIS tool. The qualitative synthesis of evidence was applied.

RESULTS

The search strategy resulted in the identification of 821 manuscripts. After removing duplicates, we screened the titles and abstracts of 552 articles, out of which 57 were selected for full-text analysis. Finally, 12 articles were included in the review. They were conducted in 6 different countries and published between the years 1997 and 2022. The number of examined women with MP ranged from 9 to 1 626.

DISCUSSION AND CONCLUSIONS

Thyroid function differs between women with MP and SP. Scarce data are available on the topic, but MPs are most likely characterized by higher HCG levels, which influences thyroid-stimulating hormone and free thyroid hormone levels. These differences are mainly expressed in the 1st trimester of pregnancy. Separate population-based reference ranges are needed to correctly diagnose thyroid diseases in MP and to avoid unnecessary treatment. Further research is needed to fill the knowledge gaps.

Evaluating health outcomes in the treatment of hypothyroidism

Clinical hypothyroidism is defined by the inadequate production of thyroid hormone from the thyroid gland to maintain normal organ system functions. For nearly all patients with clinical hypothyroidism, lifelong treatment with thyroid hormone replacement is required. The primary goal of treatment is to provide the appropriate daily dose of thyroid hormone to restore normal thyroid function for each individual patient. In current clinical practice, normalization of thyrotropin (TSH) level is the primary measure of effectiveness of treatment, however the use of a single biomarker to define adequate thyroid hormone replacement is being reevaluated. The assessment of clinical health outcomes and patient-reported outcomes (PROs), often within the context of intensity of treatment as defined by thyroid function tests (i.e., undertreatment, appropriate treatment, or overtreatment), may play a role in evaluating the effectiveness of treatment. The purpose of this narrative review is to summarize the prominent health outcomes literature in patients with treated hypothyroidism. To date, overall mortality, cardiovascular morbidity and mortality, bone health and cognitive function have been evaluated as endpoints in clinical outcomes studies in patients with treated hypothyroidism. More recent investigations have sought to establish the relationships between these end results and thyroid function during the treatment course. In addition to clinical event outcomes, patient-reported quality of life (QoL) has also been considered in the assessment of adequacy of hypothyroidism treatment. From a health care quality perspective, treatment of hypothyroidism should be evaluated not just on its effectiveness for the individual patients but also to the extent to which patients of different sociodemographic groups are treated equally. Ultimately, more research is needed to explore differences in health outcomes between different sociodemographic groups with hypothyroidism. Future prospective studies of treated hypothyroidism that integrate biochemical testing, PROs, and end result clinical outcomes could provide a more complete picture into the effectiveness of treatment of hypothyroidism.

Use of levothyroxine among pregnant women with subclinical hypothyroidism in the United Kingdom: A population-based assessment

Our study aimed to describe levothyroxine prescription patterns and trends over time among pregnant women with subclinical hypothyroidism (SCH) in the United Kingdom.

We used data from the Clinical Practice Research Datalink linked to its Pregnancy Register and the Hospital Episode Statistics database from 1998 to 2017. The study population included women with a diagnosis of SCH or an abnormal thyroid‐simulated hormone (TSH) level one year prior to or during pregnancy. We compared characteristics between women who received a prescription for levothyroxine during pregnancy and those who did not. We further described the timing, dose, duration, and temporal trends of levothyroxine prescriptions.

Our cohort included 6,757 pregnancies from 6,287 women with SCH, of whom 10% received levothyroxine during pregnancy. Among women who received levothyroxine, most received their first prescription during the first trimester (median gestational age: 7 weeks; interquartile range [IQR]: 0, 16) with a median daily dosage of 50 mcg (IQR: 50, 73). Levothyroxine prescription varied over time, decreasing from 23% of pregnant women in 1998 to 7.5% in 2003, remaining stable until 2014, and increasing to 12.5% in 2016. Smoking, diabetes, polycystic ovary syndrome, infertility, timing of SCH diagnosis, age, TSH level at diagnosis, and general practice regions were associated with prescription.

Few women with SCH received levothyroxine during pregnancy, and treatment varied by patient characteristics and geographical regions. These results highlight the need to increase awareness among healthcare providers and will guide future studies that explore barriers to initiating levothyroxine treatment for women with SCH during pregnancy.

A Clinical Debate: Subclinical Hypothyroidism

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Thyroid function testing and management during and after pregnancy among women without thyroid disease before pregnancy

BACKGROUND

Screening in pregnancy for subclinical hypothyroidism, often defined as thyroid-stimulating hormone (TSH) greater than 2.5 mIU/L or greater than 4.0 mIU/L, is controversial. We determined the frequency and distribution of TSH testing by gestational age, as well as TSH values associated with treatment during pregnancy and the frequency of postpartum continuation of thyroid hormone therapy.

METHODS

We performed a retrospective cohort study of pregnancies in Alberta, Canada. We included women without thyroid disease who delivered between October 2014 and September 2017. We used delivery records, physician billings, and pharmacy and laboratory administrative data. Our key outcomes were characteristics of TSH testing and the initiation and continuation of thyroid hormone therapy. We calculated the proportion of pregnancies with thyroid testing and the frequency of each specific thyroid test.

RESULTS

Of the 188 490 pregnancies included, 111 522 (59.2%) had at least 1 TSH measurement. The most common time for testing was at gestational week 5 to 6. Thyroid hormone therapy was initiated at a median gestational age of 7 (interquartile range 5-12) weeks. Among women with first TSH measurements of 4.01 to 9.99 mIU/L who were not immediately treated, the repeat TSH measurement was 4.00 mIU/L or below in 67.9% of pregnancies. Thyroid hormone was continued post partum for 44.6% of the women who started therapy during their pregnancy.

INTERPRETATION

The findings of our study suggest that current practice patterns may contribute to overdiagnosis of hypothyroidism and overtreatment during pregnancy and post partum.

Subclinical hypothyroidism in pregnancy

PURPOSE OF REVIEW

Subclinical hypothyroidism (SCH) is a common diagnosis among women of reproductive age. The importance of sufficient maternal thyroid supply during pregnancy is well known. Nevertheless, the effects of SCH during pregnancy and the efficacy of its treatment on maternofetal outcomes are not well established. This review discusses the recent evidence on SCH in pregnancy and how this evidence is reflected in current clinical care.

RECENT FINDINGS

Recent observational studies have found a positive association between SCH during pregnancy and adverse maternal, neonatal and offspring outcomes, mainly in thyroid peroxidase autoantibody positive women. Although interventional studies have shown a benefit of levothyroxine (LT4) treatment on selected pregnancy outcomes, there was no effect on offspring neurodevelopment.

SUMMARY

Current evidence strengthens the association between SCH with both maternofetal and offspring adverse outcomes. An earlier and more individualized diagnostic assessment taking into consideration predictors of thyroid dysfunction and major risk factors for complications could result in better management of SCH during pregnancy. The effectiveness of LT4 on improving maternofetal and long-term offspring outcomes is still not fully elucidated.