Undiagnosed thyroid disease is a common problem with significant public health implications. This is especially true during pregnancy, when the health of both the mother and the developing child can be adversely affected by abnormal maternal thyroid function. Measurement of serum thyroid stimulating hormone (TSH) and thyroid peroxidase antibodies (TPO-Ab) are two common ways to assess maternal thyroid status. The objective of our study was to determine the prevalence of abnormal TSH and TPO-Ab tests in a population of pregnant women in the Samara region of the Russian Federation. Serum samples were obtained from 1588 pregnant women as part of their routine antenatal care. TSH and TPO-Ab were measured, and trimester-specific reference values for TSH (2.5-97.5 percentiles) were calculated using TPO-Ab-negative women. TSH results outside these ranges were considered abnormal; TPO-Ab levels outside the manufacturer's reference range (>12 IU/mL) were considered abnormal. Overall, the prevalence of abnormal results was 6.3% for TSH and 10.7% for TPO-Ab. High TSH (>97.5 trimester-specific percentile) and TPO-Ab-positive results were most common in the first trimester (5.7% and 13.8%, respectively). TSH levels were associated with gestational age and TPO-Ab status, and with maternal age in TPO-Ab-negative women. TPO-Ab status was associated with both maternal and gestational age. Women with TSH >2.5 mIU/L had a significantly increased risk of being TPO-Ab-positive, and this risk increased with age. Based on our data, we conclude that abnormal TSH and TPO-Ab are common in pregnant women of the Samara region. Given the association of thyroid dysfunction to adverse pregnancy outcomes, screening of this population for abnormal thyroid function should be considered.