Abstract
A case finding strategy for thyroid dysfunction during pregnancy reflects a compromise between screening for all versus screening for none. Two randomized controlled trials (RCTs) have demonstrated a decrease in miscarriage, preterm delivery, and maternal/fetal adverse events with levothyroxine treatment (1,2). Multiple observational studies have demonstrated an increase in miscarriage in euthyroid thyroid antibody positive women (3,4) as well as preterm delivery in pregnant women with subclinical hypothyroidism (5,6). Given the data, a lack of intervention is unacceptable, but universal screening is premature in the absence of confirmatory RCTs. Accordingly, while uncertainty remains regarding a universal screening mandate, the 2011 American Thyroid Association (ATA) Thyroid and Pregnancy Guidelines strongly recommends targeted case finding (7).
Women aged 30 years or older were among the groups identified as high risk for thyroid dysfunction and in which screening should be performed. The recommendation was based on multiple studies that have demonstrated an increasing rate of hypothyroidism with increasing age (8,9). Screening all women aged 30 years and above represents an expansion of the 2000 ATA recommendation that all men and women be screened for thyroid dysfunction beginning at age 35 years (10). The 2000 ATA guidelines note that the data for this recommendation are “particularly compelling in women.” However, the guidelines did not specifically address pregnant women, a group with serious sequelae of thyroid dysfunction and in which the upper limit of normal is 2.5 mIU/L (significantly lower than the accepted upper limit of normal for nonpregnant women). Significantly, data from the National Health and Nutrition Examination Survey III (NHANES III) recently demonstrated that 10.7% of individuals between the ages of 20 and 29 years had thyrotropin values at or above 2.5 mIU/L (9). It is with all of these considerations in mind that we reiterate our strong recommendation that all women aged 30 years and above merit thyroid screening during pregnancy.
As stated in the “Future Research Directions” section of the ATA Thyroid and Pregnancy Guidelines, we noted that all screening recommendations should undergo rigorous cost-effectiveness analyses. Future recommendations on universal screening versus targeted case finding will be impacted by the results of cost-effectiveness studies, such as the study presented in October 2011 at the annual ATA meeting (11), and the outcome of ongoing prospective randomized trials presently underway in the United States, United Kingdom, and China.