Optimal Care of the Pregnant Woman with Thyroid Disease

Pregnancy has a profound impact on the thyroid gland. During a normal pregnancy the thyroid increases in size, produces 50% more T4 and T3, requires 50% more iodine, and the normal TSH range is compressed with a lower limit of normal at both ends of the spectrum. It is therefore not surprising that pregnancy has been considered a physiological stress test for the thyroid gland (1). However, what has been striking is the research over the last 20 yr linking thyroid hormonal abnormalities and thyroid autoimmunity to a wide range of adverse pregnancy, maternal, and offspring outcomes including spontaneous miscarriage, gestational hypertension, preeclampsia, gestational diabetes, postpartum thyroiditis, and decreased IQ in the offspring. The rapidly evolving literature on the interaction between the thyroid and pregnancy was the impetus for an update of the 2007 Endocrine Society Guidelines (ES-G) (2). Included in the 2012 ES-G (3) are 27 articles published since the completion of the 2007 ES-G. Using a comprehensive and scholarly process, and the product of an international committee of experts in the field, the 2012 ES-G provide 52 recommendations for the care of the pregnant woman with thyroid disorders. The authors of the 2012 ES-G should be applauded for the high quality of the recommendations and their ability to synthesize data in a complex and rapidly evolving field. The goal of guidelines in medicine is to give guidance to health care providers, assisting them in the provision of optimal patient care. Therefore, it is through the lens of both the health care professional and the patient that the 2012 ES-G will be discussed. This editorial will focus on revisions to the 2007 ES-G contained within the 2012 ES-G, a comparison with the 2011 American Thyroid Association’s thyroid and pregnancy guidelines (ATA-G) (4), the conundrum related to the fact that neither The Endocrine Society nor the American Thyroid Association represents the organization [the American College of Obstetricians and Gynecologists (ACOG)] whose members treat the vast majority of women with thyroid disease during pregnancy, the controversy regarding universal screening, and a peek into the future. The 2012 ES-G is divided, as was the 2007 ES-G, into eight sections. Important changes when comparing the 2007 to 2012 ES-G are commented on in this section. There are two noteworthy modifications in the hypothyroid section. First of all, given methodological difficulties in measuring free T4 assays during pregnancy, the guidelines, “...recommend caution in the interpretation of serum free T4 levels during pregnancy....” Alternative strategies, including the free T4 index or multiplication of the nonpregnant total T4 and T3 normal range by 1.5, are recommended. Secondly, although not a formal recommendation, the text of the 2012 ES-G states that treatment of isolated hypothyroxinemia (IH; normal TSH and a below normal T4 level), with “...partial replacement therapy may be initiated at the discretion of the caregiver, with continued monitoring.” However, from my perspective, this may result in women receiving an unproven intervention because there are no prospective data demonstrating a benefit of treating IH. Furthermore, the statement does not provide guidance to the practitioner in deciding in whom to initiate treatment and what constitutes partial replacement. In the hyperthyroidism section, the major modification relates to the recent Food and Drug Administration warning linking propylthiouracil to severe liver toxicity (5). The 2012 ES-G continues to recommend