Objective To establish the specific reference ranges of thyroid hormone for pregnant women in Fuzhou. Methods We studied retrospectively 1 658 pregnant women, who were seen at our maternity clinic and 350 non-pregnant women. The pregnant women selected did not have thyroid disorder before and were divided into three stages: first trimester(pregnancy≤12 weeks), mid-trimester pregnancy(pregnancy among 13 to 28 weeks), and late pregnancy(pregnancy beyond 28 weeks until delivery). We detected the three serum triiodothyronine(FT3), serum free thyroid(FT4),and thyroid stimulating hormone(TSH)level, then on the measurements we performed statistical analysis. Results The levels of FT3 and FT4 were declining and the level of TSH was increasing gradually. The thyroid morbidity in non-pregnant women was 6%, while the morbidity in pregnant women was 12.4%, which was much higher. The highest morbidity was subclinical hypothyroidism(4.95%), the next was low T4 blood(2.65%), and then were subclinical hyperthyroidism(2.17%), hypothyroidism(2.0%), hyperthyroidism(0.66%). Conclusion The thyroid hormone level in pregnant women changes along with the pregnancy progress. In our area the thyroid morbidity in pregnant is higher than non-pregnant women. Therefore each region should establish its specific reference ranges of thyroid hormone for normal pregnant women according to the reagents used and the detection method for screening the pregnant women.