Table 2.
Large Randomized Controlled Studies of the Effects of LT4 Treatment during Pregnancy in TPOAb-Positive Women with Normal Thyroid Function
| Study | POSTAL, 2017 | TABLET, 2019 | T4LIFE, 2022 |
|---|---|---|---|
| Country | China | United Kingdom | Netherlands |
| No. of subjects | 600 | 952 | 187 |
| Inclusion criteria | TPOAb-positive euthyroid women undergoing IVF excluding women who have experienced more than two spontaneous abortions. | TPOAb-positive euthyroid women who plan to conceive (natural pregnancy, assisted pregnancy) within 12 months, have a history of one or more miscarriages or have undergone infertility treatment. | TPOAb-positive women with normal thyroid function who had experienced two or more recurrent miscarriages. |
| Mean age | 31.3±3.9 years (LT4 group) | 32.5±4.9 years (LT4 group) | 34.9±4.2 years (LT4 group) |
| 31.7±3.8 years (control) | 32.7±4.9 years (control) | 33.7±4.7 years (control) | |
| TSH range for normal thyroid function | 0.50–4.78 mIU/L | 0.44–3.63 mIU/L | Reference value of each institution (0.30–5 mIU/L) |
| LT4 treatment methods | Initiation of LT4 treatment prior to IVF | Administration of 50 μg/day of LT4 from before conception to the end of pregnancy | Administration of LT4 before conception to the end of pregnancy |
| Starting dose of LT4 | |||
| 2.5 mIU/L≥ TSH: 50 μg/day | TSH <1.0 mU/L: LT4 0.5 μg/kg | ||
| 2.5 mIU/L< TSH: 25 μg/day (If body weight <50 kg: reduce the starting dose by 50%) | TSH 1.0–2.5 mU/L: LT4 0.75 μg/kg | ||
| TSH target: TSH 0.1–2.5 (1st), 0.2–3.0 (2nd), 0.3–3.0 (3rd) | TSH >2.5 mU/L: LT4 1.0 μg/kg | ||
| Results | Miscarriage: RR=0.97 (95% CI, 0.45–2.10) | Live birth rate (≥34 weeks): RR=0.97 (95% CI, 0.83–1.14) | Live birth rate (≥24 weeks): RR=1.03 (95% CI, 0.77–1.38) |
| Live birth rate (≥24 weeks): RR=0.98 (95% CI, 0.78–1.24) | |||
| Preterm delivery: RR=1.13 (95% CI, 0.65–1.96) | Miscarriage (<24 weeks): RR=0.95 (95% CI, 0.73–1.23) | Preterm birth (<34 weeks): RR=1.41 (95% CI, 0.33–6.08) |
LT4, levothyroxine; TPOAb, thyroid peroxidase antibody; POSTAL, Pregnancy Outcomes Study in Euthyroid Women with Thyroid Autoimmunity After Levothyroxine; TABLET, Thyroid Antibodies and Levothyroxine; IVF, in vitro fertilization; TSH, thyroid-stimulating hormone; RR, relative risk; CI, confidence interval.