Table 1.
Criteria for diagnosis of various thyroid dysfunctions in each trimester
| Category | Definition | Thyroid parameters | First trimester | Second trimester | Third trimester | |
|---|---|---|---|---|---|---|
| Trimester-specific reference range [18] | 2.5–97.5 percentile of reference population | TSH (mU/l) | 0.07–2.82 | 0.33–2.89 | 0.32–2.94 | |
| FT4 (pmol/l) | 10.48–18.49 | 9.4–14.06 | 8.5–13.54 | |||
| Overt hyperthyroidism | TSH below reference range and FT4 above | TSH (mU/l) | <0.07 | <0.33 | <0.32 | |
| FT4 (pmol/l) | >18.49 | >14.06 | >13.54 | |||
| Subclinical hyperthyroidism | TSH below reference range and normal FT4 | TSH (mU/l) | <0.07 | <0.33 | <0.32 | |
| FT4 (pmol/l) | 10.48–18.49 | 9.4–14.06 | 8.5–13.54 | |||
| Overt hypothyroidism | TSH above reference range and FT4 below | TSH (mU/l) | >2.82 | >2.89 | >2.94 | |
| FT4 (pmol/l) | <10.48 | <9.4 | <8.5 | |||
| Subclinical hypothyroidism | TSH above reference range and normal FT4 | TSH (mU/l) | >2.82 | >2.89 | >2.94 | |
| FT4 (pmol/l) | 10.48–18.49 | 9.4–14.06 | 8.5–13.54 | |||
| Isolated hypothyroxinemia | Normal TSH; FT4 below the lowest 10 percentile of reference population | TSH (mU/l) | 0.07–2.82 | 0.33–2.89 | 0.32–2.94 | |
| FT4 (pmol/l) | <11.43 | <9.97 | <9.42 | |||
| TPO-Ab positivity (TPO-Ab+ve) | TPO-Ab above cutoff value | TPO-Ab (kU/l) | ≥35 | ≥35 | ≥35 | |
| Substantially elevated TPO-Ab positivity | TPO-Ab above cutoff value | TPO-Ab (kU/l) | ≥100 | ≥100 | ≥100 | |
| Tg-Ab positivity (Tg-Ab+ve) | Tg-Ab above cutoff value | Tg-Ab (kU/l) | >115 | – | – | |
| Thyroid antibody positivity (Thy-Ab+ve) | Either TPO-Ab positivity or Tg-Ab positivity | Either TPO-Ab ≥ 35 kU/l or Tg-Ab > 115 kU/l | – | – | ||