A comparative study on outcomes of fasting vs postprandial thyroid function tests among pregnant mothers in a tertiary care setting in Sri Lanka.

Objective: Accurate estimation of serum thyrotropin (TSH) is crucial in the diagnosis of subclinical hypothyroidism (SCH) in pregnancy. We aimed to investigate whether there are significant differences between fasting and nonfasting thyroid function tests (TFTs) among pregnant mothers.

Methods: We studied 100 pregnant mothers with previously unknown thyroid dysfunction. An equal number of participants were included in each trimester. All pregnant mothers underwent fasting and 2-hour postprandial TFTs (TSH, free T4).

Results: Postprandial TSH (mean 1.01 mIU/L, SD 0.80) was significantly lower than the fasting TSH (mean 1.47 mIU/L, SD 1.18) in pregnancy (P < .01). Postprandial free T4 (mean 10.30 pmol/L, SD 2.01) was also lowered compared with fasting free T4 (mean 10.70 pmol/L, SD 1.99) in pregnancy (P < .01). The prevalence of SCH in pregnancy estimated using fasting TSH was 9.4% (SD 3%). In contrast, the prevalence was only 3.5% (SD 2%) when postprandial TSH was used.

Conclusion: Compared with the fasting state, postprandial TSH demonstrates a statistically significant reduction that greatly influences the diagnosis of SCH in pregnant mothers. Therefore, we conclude that the timing of sampling for TFTs should be standardized, especially in the pregnant population.