These cases were retrospectively reviewed, and the prevalence of birth defects was evaluated according to treatment. The authors speculated whether this finding was related to maternal thyroid function in early pregnancy [ 36 ].
A general concern about the use of iodine for the treatment of hyperthyroidism is that this treatment may be less effective than ATDs in the control of hyperthyroidism [ 6 ].
In a subsequent study from Japan [ 37 ], focus was on thyroid function in pregnant women who shifted from MMI to potassium iodide. From a clinical point, the identification of these patients is important considering the choice of treatment, but no specific predictors of this tendency to escape from the antithyroid effect of iodine could be identified in that study [ 37 ]. Further studies on the benefits and risks of treatment with potassium iodide in early pregnancy are needed including studies from populations with different levels of iodine intake.
Another pertinent question is the possibility of other treatments or the development of new treatment. This perspective of alternative treatments on the one hand and the proposal of treatment withdrawal in early pregnancy on the other hand call for further research.
Clinical studies are needed and basic scientific work is important to support the clinical data and to develop our understanding of the mechanisms by which ATDs cause teratogenic side effects. Furthermore, different types of research serve to determine the role of maternal thyroid function and the role of the autoimmune mechanisms associated with the hyperthyroidism of GD.
MMI and PTU are considered to equally cross the placenta [ 38 ], to be equally effective in the control of hyperthyroidism in pregnancy [ 39 ] and to hold the same risk of inducing fetal hypothyroidism [ 40 ]. However, more evidence is needed to unveil the mechanisms underlying their teratogenic potential. Many possible mechanisms are in play, and one may also speculate on the possible interaction between ATD, maternal and fetal thyroid function, and thyroid autoimmunity and how these various exposures may have direct or indirect adverse effects.
Current evidence substantiates a risk of birth defects associated with the use of MMI and these malformations may be severe. On the other hand, further studies are needed to settle the teratogenic role of PTU and the role of maternal thyroid function and thyroid autoimmunity. Detailed clinical data on the timing and type of exposure in early pregnancy are needed to inform clinical practice on the choice of treatment and the possibility of treatment withdrawal in selected patients.
Furthermore, basic scientific work is important to address the mechanisms underlying the development of birth defects, and to precede the development of alternative or new treatments with less severe side effects. Data sharing is not applicable to this article as no datasets were generated or analysed during the current study. Anniversary review: Antithyroid drug therapy: 70 years later.
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A comparison of propylthiouracil versus methimazole in the treatment of hyperthyroidism in pregnancy. Am J Obstet Gynecol. Download references. You can also search for this author in PubMed Google Scholar. SLA conceptualized and drafted the manuscript. SA critically reviewed, discussed, and commented on the manuscript. The author s read and approved the final manuscript. Correspondence to Stine Linding Andersen. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Ultimately, the risks for hyperthyroidism in pregnancy outweigh the risks for rare hepatic injury and embryopathy associated with these antithyroid drugs, experts said. Management with antithyroid drugs should be approached not with the goal of attaining mid-range thyroid hormone levels, but those at the upper limits of normal.
If antithyroid drugs are necessary during pregnancy, a positive trend is that the condition generally improves with treatment. But each patient is different, and the doses will need to be adjusted and monitored. Other times, the physician will be able to wean the woman off of treatment late in the second trimester, Rivkees said.
Although antithyroid drugs are ideally limited during pregnancy, other treatments are avoided altogether. Surgery is also sparingly used. In the United States, we have been stuck on using PTU for so long that many physicians are hesitant to make an adjustment. It is now prescribed about 1. Before , PTU held two-thirds of the market share, according to the researchers.
The only subgroup in which methimazole use did not increase was women of child-bearing age, 18 to 44 years. The researchers said this may reflect society and FDA recommendations about not using methimazole until the second trimester of pregnancy.
Experts Endocrine Today interviewed said further research is required to better understand the adverse effects of antithyroid drugs in pregnant hyperthyroid women.
Investigations are currently under way, though, as the recent PTU warnings have provided the topic increased attention. The American Thyroid Association and American Association of Clinical Endocrinologists are also working on updated clinical practice guidelines that will address the issue of treating hyperthyroidism during pregnancy. Is universal screening in pregnant women a beneficial, safe and cost-effective option? Healio News Endocrinology Thyroid.
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Studies do not agree if hyperthyroidism itself can increase birth defects. Studies also do not agree if PTU alone can increase birth defects. There has not been a confirmed pattern of birth defects to more strongly suggest cause from PTU exposure alone.
Additionally, other studies show no increased chance for birth defects. In summary, although studies do not agree, there is not strong evidence to say PTU clearly increases birth defects. You and your healthcare team will decide what is best for your specific situation. Hyperthyroidism has been found to increase the chance for pregnancy complications like preterm delivery delivery before week 37 and low birth weight less than 2lb 3oz.
One study did not find a higher chance of preterm delivery when PTU was used during pregnancy. It is not clear if PTU is associated with low birth weight because studies do not agree. Antithyroid medications, like PTU, or having Graves disease, can lead to too low or too high thyroid levels in a baby. Does taking PTU in pregnancy cause long-term problems in behavior or learning for the baby? Two studies looking at 44 children from preschool to adult ages whose parent took PTU during pregnancy found no difference in intelligence scores compared to their unexposed brothers or sisters.
Untreated hyperthyroidism in pregnancy can increase the chance of learning problems in children. PTU gets into breastmilk in small amounts, which means the amounts ingested by the infant are small. The American Thyroid Association has suggested that if PTU is taken while breastfeeding, doses of PTU should be limited to mg per day due to the lack of research on the chance of liver damage in the breastfed infant.
No adverse effects have been reported in babies whose mothers used PTU while breastfeeding.
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