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Peter Laurberg and Stine Linding Andersen

Thyroid hormones are essential developmental factors, and Graves’ disease (GD) may severely complicate a pregnancy. This review describes how pregnancy changes the risk of developing GD, how early pregnancy by several mechanisms leads to considerable changes in the results of the thyroid function tests used to diagnose hyperthyroidism, and how these changes may complicate the diagnosing of GD. Standard therapy of GD in pregnancy is anti-thyroid drugs. However, new studies have shown considerable risk of birth defects if these drugs are used in specific weeks of early pregnancy, and this should be taken into consideration when planning therapy and control of women who may in the future become pregnant. Early pregnancy is a period of major focus in GD, where pregnancy should be diagnosed as soon as possible, and where important and instant change in therapy may be warranted. Such change may be an immediate stop of anti-thyroid drug therapy in patients with a low risk of rapid relapse of hyperthyroidism, or it may be an immediate shift from methimazole/carbimazole (with risk of severe birth defects) to propylthiouracil (with less risk), or maybe to other types of therapy where no risk of birth defects have been observed. In the second half of pregnancy, an important concern is that not only the mother with GD but also her foetus should have normal thyroid function.

Free access

Peter Laurberg and Stine Linding Andersen

Background

Antithyroid drugs (ATDs) may have teratogenic effects when used in early pregnancy.

Objective

To review the association between the time period of ATD exposure in early pregnancy and the development of birth defects.

Methods

We identified publications on birth defects after early pregnancy exposure to the ATDs methimazole (MMI; and its prodrug carbimazole (CMZ)) and propylthiouracil (PTU). Cases of birth defects after ATD treatment had been initiated or terminated within the first 10 weeks of pregnancy were identified and studied in detail.

Results

A total of 92 publications were read in detail. Two recent large controlled studies showed ATD-associated birth defects in 2–3% of exposed children, and MMI/CMZ-associated defects were often severe. Out of the total number of publications, 17 included cases of birth defects with early pregnancy stop/start of ATD treatment, and these cases suggested that the high risk was confined to gestational weeks 6–10, which is the major period of organogenesis. Thus, the cases reported suggest that the risk of birth defects could be minimized if pregnant women terminate ATD intake before gestational week 6.

Conclusion

Both MMI and PTU use in early pregnancy may lead to birth defects in 2–3% of the exposed children. MMI-associated defects are often severe. Proposals are given on how to minimize the risk of birth defects in fertile women treated for hyperthyroidism with ATDs.

Free access

Stine Linding Andersen, Jørn Olsen and Peter Laurberg

Objective

Thyroid disorders are common in women of reproductive age, but the exact burden of disease before, during and after a pregnancy is not clear. We describe the prevalence of thyroid disease in women enrolled in the Danish National Birth Cohort (DNBC) and investigate some of its risk factors.

Design

Population-based study within the DNBC, which included 101 032 pregnancies (1997–2003).

Methods

We studied women enrolled in the DNBC who gave birth to a live-born child. Information on maternal thyroid disease (hyperthyroidism, hypothyroidism, benign goiter/nodules, thyroid cancer, and other) before, during and up to 5 years after the woman's first pregnancy in the cohort was obtained from self-report (telephone interview in median gestational week 17) and from nationwide registers on hospital diagnosis of thyroid disease/thyroid surgery (from 1977) and prescriptions of thyroid drugs (from 1995).

Results

Of the 77 445 women studied, 3018 (3.9%) were identified with an onset of thyroid disease before (2.0%), during (0.1%) or in the 5-year period after the pregnancy (1.8%). During the pregnancy, 153 (0.2%) women received antithyroid drugs and 365 (0.5%) received thyroid hormone for hypothyroidism (83 after previous hyperthyroidism, 42 after previous surgery for benign goiter/nodules or thyroid cancer). Significant risk factors for maternal thyroid disease were age, parity, origin, iodine intake, smoking, alcohol, and BMI.

Conclusions

Around 4% of Danish pregnant women had either a history of thyroid disease or thyroid disease during pregnancy or were diagnosed with thyroid disease for the first-time in the years following a pregnancy. The spectrum of thyroid disease was influenced by demographic and environmental factors.

Free access

Allan Carlé, Stine Linding Andersen, Kristien Boelaert and Peter Laurberg

Subclinical thyrotoxicosis is a condition affecting up to 10% of the population in some studies. We have reviewed literature and identified studies describing prevalences, causes and outcomes of this condition. Treatment should be considered in all subjects if this biochemical abnormality is persistent, especially in case of symptoms of thyrotoxicosis or in the presence of any complication. In particular, treatment should be offered in those subclinically thyrotoxic patients with a sustained serum TSH below 0.1 U/L. However it is important to recognise that there are no large controlled intervention studies in the field and thus there is no high quality evidence to guide treatment recommendations. In particular, there is no evidence for therapy and there is weak evidence of harm from thyrotoxicosis if serum TSH is in the 0.1–0.4 IU/L range. In this review, we describe the different causes of subclinical thyrotoxicosis, and how treatment should be tailored to the specific cause. We advocate radioactive iodine treatment to be the first-line treatment in majority of patients suffering from subclinical thyrotoxicosis due to multinodular toxic goitre and solitary toxic adenoma, but we do generally not recommend it as the first-line treatment in patients suffering from subclinical Graves’ hyperthyroidism. Such patients may benefit mostly from antithyroid drug therapy. Subclinical thyrotoxicosis in early pregnancy should in general be observed, not treated. Moreover, we advocate a general restriction of therapy in cases where no specific cause for the presumed thyroid hyperactivity has been proven.

Free access

Stine Linding Andersen, Stefan Lönn, Peter Vestergaard and Ove Törring

Objective

Antithyroid drugs (ATDs) may have teratogenic effects, but more evidence is needed on the risk and types of birth defects after the use of methimazole (MMI) and propylthiouracil (PTU). This study aimed to evaluate the association between the use of ATDs in early pregnancy and birth defects.

Design

Swedish nationwide register-based cohort study.

Methods

The study included 684 340 children live-born in Sweden from 2006 to 2012. Exposure groups defined by maternal ATD use in early pregnancy were MMI (n = 162); PTU (n = 218); MMI and PTU (n = 66); ATD before or after, but not in pregnancy (n = 1551) and non-exposed (never ATD (n = 682 343)). Outcome was cumulative incidence of birth defects diagnosed before two years of age.

Results

The cumulative incidence of birth defects was not significantly different in children exposed to MMI (6.8%, P = 0.6) or PTU (6.4%, P = 0.4) vs non-exposed (8.0%). For subtypes of birth defects, MMI was associated with an increased incidence of septal heart defects (P = 0.02). PTU was associated with ear (P = 0.005) and obstructive urinary system malformations (P = 0.006). A case of choanal atresia was observed after exposure to both MMI and PTU. The incidence of birth defects in children born to mothers who received ATD before or after, but not in pregnancy, was 8.8% and not significantly different from non-exposed (P = 0.3), MMI exposed (P = 0.4) or PTU exposed (P = 0.2).

Conclusions

MMI and PTU were associated with subtypes of birth defects previously reported, but the frequency of ATD exposure in early pregnancy was low and severe malformations described in the MMI embryopathy were rarely observed.

Free access

Stine Linding Andersen, Allan Carlé, Jesper Karmisholt, Inge Bülow Pedersen and Stig Andersen

Fetal programming is a long-standing, but still evolving, concept that links exposures during pregnancy to the later development of disease in the offspring. A fetal programming effect has been considered within different endocrine axes and in relation to different maternal endocrine diseases. In this critical review, we describe and discuss the hypothesis of fetal programming by maternal thyroid dysfunction in the context of fetal brain development and neurodevelopmental disorders in the offspring. Thyroid hormones are important regulators of early brain development, and evidence from experimental and observational human studies have demonstrated structural and functional abnormalities in the brain caused by the lack or excess of thyroid hormone during fetal brain development. The hypothesis that such abnormalities introduced during early fetal brain development increase susceptibility for the later onset of neurodevelopmental disorders in the offspring is biologically plausible. However, epidemiological studies on the association between maternal thyroid dysfunction and long-term child outcomes are observational in design, and are challenged by important methodological aspects.