Thyroid function tests in pregnancy

The recognition of abnormality in thyroid function tests during pregnancy is important for the welfare of the mother as well as fetus. The values of serum tri-iodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH) in nonpregnant women are not applicable during pregnancy and also differ in iodine deficient areas. In the present study, one hundred and twenty-four apparently normal, healthy young primigravidas with no known metabolic disorders and normal carbohydrate gestational intolerance test, consecutively attending the antenatal clinic were included in the study. The serum tri-iodothyronine (T3), thyroxine (T4) and thyroid-stimulating hormone (TSH) in these women were estimated. In the first trimester, the mean T3 values were found to be 1.85 nmol/L, which increased to a mean of 2.47 nmol/L in the second trimester and declined in the third trimester to 1.82 nmo/L. Mean T4 levels were also seen to rise from 164.50 nmol/L in the first trimester to 165.80 nmol/L in the second trimester and then decreased in the third trimester to 159.90 nmol/L. Mean TSH levels were seen to rise progressively through the three trimesters of pregnancy from 1.20 microlU/ ml in the first trimester to 2.12 microlU/ml in the second trimester and further to 3.30 microlU/ml in the third trimester of pregnancy. Three asymptomatic pregnant women (2.5%) were found to have abnormal TSH values with normal T3 and T4 levels and good obstetric outcome. This pilot study also indicates the range to T3 as 1.7 - 4.3 nmol/L in second trimester and 0.4 - 3.9 nmol/L in third trimester, T4 as 92.2 - 252.8 nmol/L in second trimester and 108.2 - 219.0 nmol/ L in third trimester, and TSH as 0.1 - 5.5 microlU/ml in second trimester and 0.5- 7.6 microlU/ml in third trimester of pregnancy.