Association and Predictive Accuracy of High TSH Serum Levels in First Trimester and Adverse Pregnancy Outcomes. Schneuer FJ, preterm birth; 0.70 (95% CI, 0.61-0.79) for miscarriage; and 0.63 (95% CI, 0.60-0.65) for any adverse pregnancy outcome. High TSH serum levels during the first trimester of pregnancy were associated with adverse pregnancy outcomes; however, the predictive accuracy was poor. Screening for high TSH levels in the first trimester would be of no benefit to identify women at risk. COMMENT-This is an important study on TSH screening in pregnancy, because of the size of the sample , and the analysis. No data is available on T4 levels, or antibodies. No interventions were made by the investigators, and no information is available on treatments of the subjects during pregnancy. The TSH assay results were not directly linked to patient outcomes records, but the investigators were able to relate outcomes via “probabilistic linking methods” on 93.7% of subjects with a stated error of <1%. TSH above the 95th centile was positively associated with Small for Gestational Age, preterm birth, miscarriage, and any adverse pregnancy outcome. Rates of preterm births, (5.1%), SGA (7.8%) and pre-eclampsia (2.6%) were about 20% lower than experienced in the general population, presumably because this was a “relatively healthy” self-selected population. Only 0.14% of samples had TSH=/> 10. Miscarriages were “under-reported”. However the important point is made that the predictive value of an elevated TSH for an adverse outcome was low, logically because adverse outcomes arise from multiple causes, not just an elevated TSH. Although having a variety of problems, this study appropriately raises a cautionary note on TSH screening. We eagerly await the outcome of ongoing interventional trials.