Screening in Pregnancy. Because of the findings in the studies from 1999 cited above, some professional organizations began to recommend routine prenatal screening and treatment for subclinical hypothyroidism. Consequent to the Lazarus study, however, clinical practice guidelines from the Endocrine Society, the American hyroid Association, and the American Association of Clinical Endocrinologists uniformly recommended screening only those at greater risk during pregnancy (De Groot, 2012; Garber, 2012). his has been and still is the recommendation of the American College of Obstetricians and Gynecologists (2017). he indings of Casey and colleagues (2017) further buttress these recommendations.
Women with low serum free T4 values but a normal-range TSH level are considered to have isolated matenal hypothyroxinemia.
Its incidence in two large trials was l.3 to 2.1 percent (Casey, 2007; Cleary-Goldman, 2008). As shown in Figure 58-2, unlike in subclinical hypothyroidism, these women had a low preva lence of antithyroid antibodies.
Evolution of the knowledge of this thyroid disorder was similar to that seen with subclinical hypothyroidism. Initial studies reported that ofspring of women with isolated hypothyroxinemia had neurodevelopmental diiculties (Kooistra, 2006; Pop, 1999, 2003). In another study, Casey and colleagues (2007) found no higher risks for other adverse perinatal outcomes compared with those of euthyroid women. Also, the aforementioned CATS study did not ind improved neurodevelopmental outcomes in women with isolated hypothyroxinemia who were then treated with thyroxine (Lazarus, 2012).
he randomized trial conducted by the Maternal-Fetal Medicine Units Network also provided data to settle this question. Casey and colleagues (2017) noted no higher rates of adverse outcomes between groups and found that early thyroxine treatment ofered no beneits (see Table 58-5).
Autoantibodies to TPO and thyroglobulin have been identiied in 6 to 20 percent of reproductive-aged women (Thangaratinam, 201l). Most who test positive for such antibodies,
TABLE 58-5. Pregnancy and Perinatal Outcomes According to Diagnosis and Treatment Group of Thyroid Disordersa
EGA at delivery (weeks) 39.1 ± 2.5 38.9 ± 3.1 39.0 ± 2.4 38.8 ± 3.1 birth <34 weeks 9.1 % 10.9% 3.8% 2.7% Placental abruption 0.3% 1.5% 1.1% 0.8%
Preeclampsia 6.5% 5.9% 3.4% 4.2%
Diabetes 7.4% 6.5% 8.0% 9.2%
NICU admission 8.6% 6.2% 11.8% 11.9%
Birthweight < 10th centile 9.8% 8.1 % 8.8% 7.8% IQ median (25th, 75th 97 (85,105) 94 (85,107) 94(83,101) 91 (82,101) dFor all comparisons, p >0.05.
EGA = estimated gestational age; IQ = intelligence quotient; [lICU = neonatal intensive care unit. Data from Casey, 201r7.