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TSH reference higher in pregnant Chinese women during first trimester
Among Chinese pregnant women, researchers found that serum thyroid-stimulating hormone was significantly higher from 4 to 6 weeks than 7 to 12 weeks, suggesting the potential need for two reference ranges of thyroid function during early pregnancy.
Researchers measured serum TSH in 4,800 pregnant women from three cities in the Liaoning Province of China during their first trimester as well as 2,000 women who planned to become pregnant. They also assessed 535 pregnant women in the second and third trimesters during follow-up.
Results revealed a higher median TSH from 4 to 6 weeks gestation (2.15 mIU/L; 95% CI, 0.56-5.31) vs. 7 to 12 weeks (1.47 mIU/L; 95% CI, 0.1-4.34), with a significant decrease from the seventh week thereafter. The researchers, however, observed no significant difference in TSH when compared with nonpregnant women (2.07 mIU/L; 95% CI, 0.69-5.64).
Of the 4,800 pregnant women, prevalence of subclinical hypothyroidism was 27.8% using a diagnostic criteria of TSH >2.5 mIU/L and 4% using the reference interval derived from the researchers’ laboratory (0.14 mIU/L to 4.87 mIU/L). Of the 118 pregnant women with serum TSH >2.5 mIU/L in the first trimester, only 30% and 20.3% had TSH >3 mIU/L at the 20th and 30th week of gestation, according to the study results.
Data indicated no significant change in free T4 during the first trimester.
“This observation led us to demonstrate, for the first time, that two reference ranges should be established in the first trimester for assessment of thyroid function: 4 to 6 weeks and 7 to 12 weeks of gestation,” the researchers wrote. “For early pregnant women, the reference range should be chosen corresponding to the gestational week. The reference range for nonpregnant women can be used for assessment of pregnant women during the 4 to 6 gestational weeks.”
Disclosure: The researchers report no relevant financial disclosures.