813: Pregnancy outcomes in women with elevated free triiodothyronine (fT3) during the first half of pregnancy

Abstract

813 Pregnancy outcomes in women with elevated free triiodothyronine (fT3) during the first half of pregnancy Carmen Tudela, Brian Casey, Donald McIntire, F. Gary Cunningham University of Texas Southwestern Medical Center, Obstetrics and Gynecology, Dallas, TX, The University of Texas Southwestern Medical Center, Obstetrics and Gynecology, Dallas, TX OBJECTIVE: To assess pregnancy outcomes in women identified with elevated fT3 levels during the first half of pregnancy and compare them to euthyroid women with normal range fT3 levels. STUDY DESIGN: Between November 2000 and April 2003, all women who presented for prenatal care underwent thyroid screening. Excess serum was frozen and stored at -80 degrees Celsius. Samples from 17,298 women without clinical hypothyroidism and who had been screened in the first 20 weeks of gestation and delivered a singleton infant weighing 500g or more were analyzed using a chemiluminescent assay for multiple thyroid analytes including fT3. Pregnancy outcomes in women with fT3 values above the 97.5th percentile for gestational age were compared to women with fT3 values greater than the 2.5th and less than the 97.5th percentiles. Pregnancy outcomes in these women were further stratified according to thyrotropin (TSH) level and risk. RESULTS: The upper thresholds for fT3 ranged from 5.08 to 6.05 pg/mL during the first half of pregnancy. When compared to women with normal fT3 (n 16,430) those with elevated fT3 (n 434) were at increased risk for fetal death (1% vs. 0.5%, P 0.012) See figure below for odds of fetal death according to fT3 and stratified by TSH level. CONCLUSION: Isolated elevated fT3 values during pregnancy are associated with an increase in perinatal mortality. This difference persists in women with a normal TSH and high fT3.