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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Thyroid Disorders in Pregnancy
Sponsored by The Indian Health Service Clinical Support Center
6. Hypothyroidism (2)
Case Scenario
Agnes Naakai is a 34 y/o G3P2 at 19 weeks gestation with known hypothyroidism who is taking levothyroxine 0.2 mg daily. She has no complaints. Physical examination is unremarkable. Her initial thyroid functions are reported as follows:
TSH: 17.2 mIU/mL (nl: 0.46-4.68)
Free T4: 0.70 ng/dL (nl: 0.78-2.19)
Should you take any action? What would be most appropriate?
Hypothyroidism remains a frequent diagnosis in general medicine. While severe hypothyroidism may impair fertility, most hypothyroid women who are on replacement therapy will be able to become pregnant. The lassitude, weight gain, constipation, and other symptoms that may be seen during normal pregnancy may suggest hypothyroidism as a potential diagnosis.
Postpartum fatigue symptoms are even more suggestive of this possibility, and indeed, the postpartum period is often when the diagnosis of hypothyroidism is first made. Postpartum thyroid dysfunction may be transient or permanent. Finding a high TSH and a low free T4 will then usually make the diagnosis.
Most patients already diagnosed with hypothyroidism are receiving thyroxine replacement when first seen and are usually asymptomatic. Thyroxine requirements usually go up by about 50 micrograms during pregnancy as a result of increased thyroid binding globulin (TBG), the increased metabolic demands of pregnancy, and the increased volume of distribution.
It is best to check TSH and free T4 each trimester. Occasionally you will find a patient who demonstrates how hard their gland is working to keep them euthyroid: they will have a normal free T4 but a high TSH. Such women need an increment in their supplemental thyroxine. Changes in therapy usually will not be manifested for at least 4-6 weeks, so it is not necessary to check labs more frequently than this after a dosage change.
Haddow et al reported that protracted untreated maternal hypothyroidism may result in adverse fetal effects in terms of neurologic development and has been demonstrated to result in lower subsequent childhood intelligence quotients. Some subsequently proposed that all pregnant women be tested for hypothyroidism to avoid this sequence of events, but ACOG noted that there are insufficient data to warrant routine screening of asymptomatic pregnant women for hypothyroidism at this time.
