This Article Full Text Full Text (PDF) A correction has been published All Versions of this Article: 93/9/3341    most recent Author Manuscript (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Google Scholar Articles by Haddow, J. E. PubMed PubMed Citation Articles by Haddow, J. E. Related Collections Thyroid Female Endocrinology

Variability in Thyroid-Stimulating Hormone Suppression by Human Chronic Gonadotropin during Early Pregnancy

The Warren Alpert Medical School of Brown University (J.E.H., M.R.M., G.L.-M., G.E.P., J.A.C.), Providence, Rhode Island 02903; Columbia University College of Physicians and Surgeons (J.C.-G., F.D.M., M.E.D.), New York, New York 10027; Royal College of Surgeons in Ireland (F.D.M.), Dublin 2, Ireland; University of Utah and Intermountain HealthCare (T.F.P.), Salt Lake City, Utah 84111; Swedish Medical Center (D.A.N.), Seattle, Washington 98122; and Montefiore Medical Center/Albert Einstein College of Medicine (P.B.), Bronx, New York 10461

Address all correspondence and requests for reprints to: James E. Haddow, M.D., Director, Division of Medical Screening, Women & Infants Hospital, 70 Elm Street, 2nd Floor, Providence, Rhode Island 02903. E-mail: jhaddow{at}ipmms.org.

Objective: The objective of the study was to further explore relationships between human chorionic gonadotropin (hCG), TSH, and free T₄ in pregnant women at 11 through 18 wk gestation.

Study Design: The design of the study was to analyze hCG in comparison with TSH and free T₄, in paired first- and second-trimester sera from 9562 women in the First and Second Trimester Evaluation of Risk for Fetal Aneuploidy trial study.

Results: hCG is strongly correlated with body mass index, smoking, and gravidity. Correlations with selected maternal covariates also exist for TSH and free T₄. As hCG deciles increase, body mass index and percent of women who smoke both decrease, whereas the percent of primigravid women increases (P < 0.0001). hCG/TSH correlations are weak in both trimesters (r² = 0.03 and r² = 0.02). TSH concentrations at the 25th and fifth centiles become sharply lower at higher hCG levels, whereas 50th centile and above TSH concentrations are only slightly lower. hCG/free T₄ correlations are weak in both trimesters (r² = 0.06 and r² = 0.003). At 11–13 wk gestation, free T₄ concentrations rise uniformly at all centiles, as hCG increases (test for trend, P < 0.0001), but not at 15–18 wk gestation. Multivariate analyses with TSH and free T₄ as dependent variables and selected maternal covariates and hCG as independent variables do not alter these observations.

Conclusions: In early pregnancy, a woman’s centile TSH level appears to determine susceptibility to the TSH being suppressed at any given hCG level, suggesting that hCG itself may be the primary analyte responsible for stimulating the thyroid gland. hCG affects lower centile TSH values disproportionately.