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PURPOSE OF REVIEW: The purpose of this review is to summarize recent information that has had a significant impact on the laboratory diagnosis and clinical management of newborns with congenital hypothyroidism and congenital adrenal hyperplasia (CAH). RECENT FINDINGS: An approximate doubling of the incidence rate of congenital hypothyroidism in many parts of the world has been attributed to increased detection of infants with mild disease, delayed thyroid stimulating hormone elevations and demographic changes. A substantial number of children with modest thyroid stimulating hormone elevations on screening have permanent disease. Circulating levels of thyroxine may vary among hypothyroid children who are given identical dosages of medication. Treated infants should be monitored every 1-2 months during the first year of life. Although, generic and brand name thyroxine preparations may not be bioequivalent, children can be well controlled on generic formulations.Enzyme linked immunoassay assay for 17-hydroxyprogesterone is associated with a high rate of false positive specimens. In attempts to minimize this problem, some programs have resorted to two-tier screening of the initial specimen with steroid profiling as the second tier. Several programs are routinely testing second specimens in an effort to reduce the incidence of missed CAH cases. SUMMARY: This review explains the uptick in incidence rate of congenital hypothyroidism and underscores issues in management that can affect developmental outcome. One specimen two-tier testing for CAH resulted in an increased false negative rate without significantly reducing the false positive rate. The benefit of collecting second specimens for CAH screening is problematic. Optimal treatment of CAH continues to pose a challenge.

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OBJECTIVE: The incidence of congenital hypothyroidism (CH) detected by newborn screening in the US has increased significantly since the early 1990s. We defined the characteristics associated with the increased incidence. PATIENTS: A cohort of children with CH born during an earlier period of low incidence (1991-94) was compared with a cohort born during a later period when the incidence of CH had doubled (2001-04). MEASUREMENTS: Screening was performed with T4 as the primary marker and thyroid stimulating hormone (TSH) on selected specimens. Follow-up on hypothyroid children determined whether they had permanent or transient hypothyroidism. Cases were classified based on laboratory results: initial TSH ≥100 mU/l was 'severe,' initial TSH <100 mU/l but ≥20 mU/l was 'mild' and initial TSH <20 mU/l with subsequent abnormal TSH was 'delayed'. RESULTS: The overall incidence of CH almost doubled between the two time periods, from 1:3010 to 1:1660. Excess cases were found in the mild and delayed categories, with no increase in severe cases. The proportion of transient cases was <5% in severe cases, 40% in mild cases and 70% among delayed cases. There was no difference in the proportion of transient case between the two time periods. Modifications to the T4/TSH testing protocol between the two time periods resulted in substantially increased numbers of specimens in the younger cohort being selected for TSH testing in both initial and repeat specimens. CONCLUSION: The rising incidence of CH in Massachusetts is confined to mild and delayed cases. Our findings suggest that this rise is attributable to enhanced detection rather than an absolute increase in numbers.

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OBJECTIVE: To test the hypothesis that very low birth weight (VLBW) and extremely low birth weight (ELBW) infants have an increased incidence of congenital hypothyroidism (CH) with a delayed thyroid-stimulating hormone (TSH) elevation and that the outcomes of these infants are similar to control infants. STUDY DESIGN: Retrospective analysis of newborn thyroid screening data for 92 800 live births in Rhode Island to identify CH with a delayed TSH elevation. Developmental, growth, and endocrine outcomes of the index cases were assessed at 18 months corrected age. RESULTS: CH with a delayed TSH elevation occurred in 1 in 58 ELBW, 1 in 95 VLBW, and 1 in 30 329 infants weighing ≥1500 grams (P < .0001). The incidence of head circumference <10(th) percentile was higher in VLBW infants with CH associated with a delayed TSH elevation (P < .05), and the mean head circumferences, weights, lengths, and developmental scores were similar to matched control infants. Three infants received short-term levothyroxine replacement. CONCLUSIONS: The incidence of CH with a delayed TSH elevation was higher in ELBW and VLBW infants compared with infants weighing ≥1500 grams. The outcomes of these infants were comparable with matched control infants.

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CONTEXT: Thyroid hormone is essential for normal brain development. Limited data are available regarding whether thyroid function in neonates influences later cognitive development. OBJECTIVE: Our objective was to study associations of newborn T4 levels with maternal thyroid function and childhood cognition. DESIGN AND SETTING: We studied participants in Project Viva, a cohort study in Massachusetts. PARTICIPANTS: We studied a total of 500 children born 1999--2003 at 34 wk or more. MAIN OUTCOME MEASURES: We determined cognitive test scores at ages 6 months and 3 yr. RESULTS: Mean newborn T4 at a mean age of 1.94 d was 17.6 (sd 4.0) microg/dl, and levels were higher in girls [1.07 microg/dl; 95% confidence interval (CI) 0.38, 1.76] and infants born after longer gestation (0.42 microg/dl; 95% CI 0.17, 0.67 per wk). Newborn T4 levels were not associated with maternal T4, TSH, or thyroid peroxidase antibody levels. On multivariable linear regression analysis, adjusting for maternal and child characteristics, higher newborn T4 was unexpectedly associated with poorer scores on the visual recognition memory test among infants at age 6 months (-0.5; 95% CI -0.9, -0.2), but not with scores at age 3 yr on either the Peabody Picture Vocabulary Test (0.2; 95% CI -0.1, 0.5) or the Wide Range Assessment of Visual Motor Abilities (0.1; 95% CI -0.2, 0.3). Maternal thyroid function test results were not associated with child cognitive test scores. CONCLUSIONS: Newborn T4 concentrations within a normal physiological reference range are not associated with maternal thyroid function and do not predict cognitive outcome in a population living in an iodine-sufficient area.

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The fetus is totally dependent in early pregnancy on maternal thyroxine for normal brain development. Adequate maternal dietary intake of iodine during pregnancy is essential for maternal thyroxine production and later for thyroid function in the fetus. If iodine insufficiency leads to inadequate production of thyroid hormones and hypothyroidism during pregnancy, then irreversible fetal brain damage can result. In the United States, the median urinary iodine (UI) was 168 microg/L in 2001-2002, well within the range of normal established by the World Health Organization (WHO), but whereas the UI of pregnant women (173 microg/L; 95% CI 75-229 microg/L) was within the range recommended by WHO (150-249 microg/L), the lower 95% CI was less than 150 microg/L. Therefore, until additional physiologic data are available to make a better judgment, the American Thyroid Association recommends that women receive 150 microg iodine supplements daily during pregnancy and lactation and that all prenatal vitamin/mineral preparations contain 150 microg of iodine.

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Previous studies have disclosed that a substantial percentage of infants from mothers with thyroid autoimmunity have antibodies to thyroid peroxidase (TPOAb) at birth. Furthermore, these antibodies have been shown to be of maternal origin. In view of this we thought it would be of interest to determine the prevalence of TPOAb in newborns from an unselected population of women. This was done by retrieving stored dried blood specimens from 240 full-term healthy infants, which had been obtained during 1999 for routine newborn screening. Ten percent of the randomly selected specimens tested TPOAb positive. Thyroid function in the mothers could not be evaluated because all specimens had been tested anonymously. In summary, our results indicate that a significant percentage of newborns were TPOAb positive. It is unclear at this time whether such antibodies reflected maternal thyroid autoimmunity and/or other autoimmune disorders. However, the close association between autoimmune thyroid disease and TPOAb positivity raises the possibility of abnormal thyroid function in some of the mothers.

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