Panesar Ns, et al. Reference intervals for thyroid hormones in pregnant Chinese women. Ann Clin Biochem. 2001;. MEDLINE 16. Castracane VD and Gimpel T. Reference Values in Pregnancy for IMMULITE Assays.
Brent GA. Maternal Thyroid function: Interpretation of thyroid function tests in pregnancy. Clin Obstet Gynecol. 1997;. 12. Mori M, et rning sickness and thyroid function in normal pregnancy. Obstet Gynecol. 1988 Sep;72(3 Pt 1 355-9.
Whereas serum free T4 and free T3 gradually decrease during pregnancy 4,7. While the values for most thyroid function tests generally lie within normal non-pregnant ranges. Some investigastors have found free T4 concentrations 8 and TSH 9 to fall below the lower limit of the normal range using newer assays.
DPC Technical Report. 1999. Accessed Created: Mark Curran, M.D. Updated: Mark Curran, M.D).
This includes both bound and free hormone. Elevated estrogen levels during pregnancy cause thyroid binding globulin (TBG) levels to rise. Because the majority of T4 and T3 circulates bound to TBG the total T4 and total T3 measurements will also rise, but the levels of free T4 and fee T3 will not be affected.
BACKGROUND AND METHODS : Women with hypothyroidism have been thought not to require an increase in thyroxine replacement during pregnancy. To evaluate the effects of pregnancy on thyroxine requirements, we retrospectively reviewed the thyroid function of 12 women receiving treatment for primary hypothyroidism before, during, and after pregnancy.
Because of high thyrotropin levels, the thyroxine dose was increased in 9 of the 12 patients. Among the three patients who did not require an increased thyroxine dose were two with low serum thyrotropin levels before pregnancy, suggesting excessive replacement at that time.
J Clin Endocrinol Metab 2000;. 7. Amerlex free triiodothyronine and free thyroxine levels in normal pregnancy. Br J Obstet Gynaecol. 1985;. 8. McElduff A Measurement of free thyroxine (T4) levels in pregnancy.
Although the effects of this modest level of hypothyroidism are not known, we think it prudent to monitor thyroid function throughout gestation and after delivery and to adjust the thyroxine dose to maintain a normal serum thyrotropin level.
The resin T3 uptake value is reduced as expected during pregnancy Hyperthyroid Profile Test Result Units Reference Range T4 Total 27 ug/dl T3 Uptake 29.6 FT4 Index 8.0 ug/dl TSH 0.019 uIU/ml The suppressed TSH, and serum total T4 above the "normal range for pregnancy" (approximately 9-18 mg/dl, 120-240 nmol/L) are consistent with hyperthyroidism.
This remained the case when the measurement was made by a dialysis kit method. These results challenge the current widely-accepted statement that free T4 concentrations remain within the normal nonpregnant range during pregnancy.
Test Abbreviation Typical Ranges Serum thyroxine T4 ug/dl. Free thyroxine fraction FT4F Free Thyroxine FT4 ng/dl. Thyroid hormone binding ratio THBR Free Thyroxine index FT4I 4-11. Serum Triiodothyronine T3 80-180 ng/dl Free Triiodothyronine l FT pg/d.
The T3 is increased in almost all cases of hyperthyroidism and usually goes up before the T4 does. The T3 is decreased during acute illness and starvation, and is affected by several medications including Inderal, steroids and amiodarone.
Pregnancy Serum Units first trimester second trimester third trimester Reference Free T3 pmol/L 3 - 5.7 2.8 - 4.2 2.4 - 4.1 15 Free T4 ng/dL 0.86 - 1.87 0.64 - 1.92 0.64 - 1.92 16 pmol/L 11.1 - 24.1 8.2 - 24.7 8.2 - 24.7 15 ng/dL 0.86 - 1.77 0.63 - 1.29 0.66.
A longitudinal study of serum TSH and total and free iodothyronines during normal pregnancy. Acta Endocrinol 1982;. 5. Pedersen KM, et al. Amelioration of some pregnancy associated variation in thyroid function by iodine supplementation.
Third Trimester:.43 - 2.78 MORE INFORMATION For more information on the effects of maternal thyroid dysfunction in pregnancy, see the following selected resources: Source: Soldin, Offie, "Thyroid Function Testing in Pregnancy and Thyroid Disease: Trimester Specific Reference Interfals.
A summary of key points: Thyroid disorders - both overt, and sublinical/borderline - are associated with pregnancy complications and both short- and long-term health implications for both mother and child. The risks are greater for women who have autoimmune thyroid disease, even if the thyroid levels are normal euthyroid.