What healthcare providers should know about detecting thyroidal conditions
By Sarah L. Berga, MD
Professor and Chair
Department of Obstetrics and Gynecology
Vice President for Women's Health Services
Wake Forest Baptist Health
Thyroid dysfunction and disease might present as reproductive compromise including oligomenorrhea, infertility, and miscarriage. Thyroid dysfunction and disease might complicate pregnancy and lead to compromised fetal neurodevelopment and preterm labor. Infertility procedures, particularly controlled ovarian hyperstimulation and ovulation induction with gonadotropins, increase the thyroxine requirement before the establishment of pregnancy. As such, the detection of thyroidal conditions may fall to any provider who cares for women.
Although we think of thyroid disease as a simple condition in which thyroxine is given when the thyroid-stimulating hormone (TSH) level is elevated and then TSH levels are monitored to see if the patient is getting the correct amount, it is a bit more complex than that. Indeed, the American Thyroid Association released a 45-page document titled "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and Postpartum," which contains 76 recommendations.1 The document was endorsed by the American Congress of Obstetricians and Gynecologists, among other groups.
The introduction highlights a few key points. During pregnancy, the thyroid gland increases 10%-20% in size and the production of thyroxine (T4) and triiodothyronine (T3) increases by 50% along with a 50% increase in the daily iodine requirement. The range of TSH is decreased throughout pregnancy because of the actions of hCG, and thus the upper and lower limits of TSH must be adjusted to detect and treat thyroidal disease. Approximately 10%-20% of pregnant women have antibodies to the thyroid gland during the first trimester and therefore are at high risk of developing overt hypothyroidism during pregnancy. I would add that it long has been known that symptoms such as fatigue are not a good way to screen for thyroid disease in the non-pregnant state, but fatigue is the sine qua non of pregnancy, so the only way to know if a pregnant patient's fatigue is partly related to subclinical or overt hypothyroidism is to screen.
Some of the recommendations of the report are highlighted below:
- Recommendation 2 states that "If trimester-specific reference ranges for TSH are not available, the following reference ranges are recommended: first trimester 0.1-2.5 mIU/L; second trimester 0.2-3.0 mIU/L; and third trimester 0.3-3.0 mIU/L.
- Recommendations 4 and 5 make the point that the wide variation in free T4 methodologies renders TSH a more reliable indicator of thyroidal status during pregnancy than FT4.
- Recommendation 6 is straightforward. Overt hypothyroidism should be treated in pregnancy using the TSH ranges above as guidance for how much thyroxine to give.
- Recommendations 8 and 9 grapple with the gray area of subclinical hypothyroidism (SCH), noting that SCH has been associated with adverse maternal and fetal outcomes. There is insufficient evidence from randomized controlled trials (RCTs) to recommend for or against universal levo-thyroxine replacement (LT4) in thyroid antibody negative women with SCH. However, women with SCH who are thyroid antibody positive should be treated with LT4.
- Treated hypothyroid patients already receiving LT4 who are newly pregnant should independently increase their dose of LT4 by 25%-30% immediately upon missed menses or positive home pregnancy test. There is great inter-individual variation in the amount of LT4 needed to maintain TSH below 2.5 mIU/L in the first trimester. (Recommendations 13 to 15).
- Euthyroid women who are thyroid antibody positive and not treated with LT4 should be monitored every four weeks during the first half of pregnancy and at least once between 26 and 32 weeks gestation (Recommendation 20).
- Recommendation 63 advises that women with postpartum depression should be evaluated for autoimmune thyroiditis with TSH, FT4, and thyroid peroxidase antibodies (TPOAb).
- Recommendation 72 states that there is insufficient evidence to recommend for or against universal screening with TSH during the first trimester. However, recommendation 76 suggests that serum TSH be evaluated early in pregnancy to screen for those at high risk for overt hypothyroidism. High-risk factors include: history of thyroid dysfunction or prior thyroid surgery, age > 30 years, symptoms, goiter, TPOAb positive, type 1 diabetes, any autoimmune disorder, history of miscarriage or preterm delivery, history of head or neck radiation, family history of thyroid dysfunction, obesity > 39 kg/m2, use of amiodarone, lithium, recent iodinated radiologic contrast, infertility, and residing in an area of moderate to severe iodine insufficiency.
It would seem that all but the most straightforward of patients should be considered at risk and, therefore, screened. I suspect that by recommendation 72, you already were feeling that the detection and treatment of thyroidal conditions had morphed into a complicated topic. However, if recommendations 1 through 75 were not enough to convince you that this is not an entirely straightforward topic, then reading the rather long list of who is considered high risk and therefore eligible for screening probably was the drop that caused the flood. If all women > 30 years are at high risk, then it is starting to look far simpler and less time intensive to screen. TSH, with or without FT4, is inexpensive, particularly when compared to some of the screening tests we already perform universally. Also, as I noted earlier, if symptoms such as fatigue and goiter are used as criteria to determine who should be screened, then we are pushed even closer toward universal screening because which pregnant woman is not fatigued and which does not have an increase in thyroid size?
I remember an adage that a mind is a terrible resource to waste. What we know about fetal neurodevelopment and its dependence on appropriate maternal thyroxine supply shifts us in favor of accurate detection. Although we might lack sufficient evidence from RCTs to make a strong recommendation for universal screening, there is a lot of other evidence from the molecular and cellular investigations and even screening trials2 to suggest that fetal neurodevelopment depends critically on appropriate maternal thyroxine. Let us not forget that the mother is the sole source of fetal thyroxine during the first trimester and the predominant source even in the second and third trimesters. Finally, I would be remiss to not mention another article released in July 2011 showing that the development of fetal goiter in mothers on antithyroid drugs for Grave's hyperthyroidism responds better to intra-amniotic thyroxine than discontinuing the anti-thyroid drugs.3 The authors suggest that centralized care of pregnant women with Grave's disease is urgently needed to maintain optimal fetal development.
Screening guidelines are helpful, but they are a work in progress. When routine screening was conducted, 2%-3% of pregnant women had an elevated serum TSH. Also, if subclinical maternal HYPERthyroidism is not associated with adverse maternal or fetal outcomes4 and maternal hypothyroidism is, then it would seem better generally to err on the side of too much thyroxine to the fetus than too little. Not only is TSH a relatively inexpensive test, thyroxine is a relatively inexpensive medication.
- Stagnaro-Green A, Abalovich M, Alexander E, et al. Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid 2011; 21:1-46. Doi: 10.1089/thyr2011.0087.
- Haddow JE, Palomaki GE, Allan WC, et al. Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child. NEJM 1999; 341:549-555.
- Bliddal S, Krogh Rasmussen A, Sundberg K, et al. Antithyroid drug-induced fetal goitrous hypothyroidism. Nat Rev Endocrinol 2011;7:396-406, 2011. Doi: 10.1038/nrendo.2011.34.
- Casey BM, Dashe JS, Wells CE, et al. Subclinical hyperthyroidism and pregnancy outcomes. Obstet Gynecol 2006; 107:337-341.