Hypothyroidism
24
Recommendations Table 12. Isolated Hypothyroxinemia
Preconception and in Pregnancy
Strength
*
Level
#
For maternal isolated hypothyroxinemia diagnosed in the
first trimester, do not offer levothyroxine treatment.
Conditional Low
For maternal isolated hypothyroxinemia diagnosed aer the
first trimester, levothyroxine treatment should not be offered.
Strong High
* Strength of Recommendation;
#
Level of Evidence; Good Practice Statement.
Box 4. Perinatal TgAb Positivity and Other Signs of Thyroid
Autoimmunity
TgAb positivity is a reflection of thyroid autoimmunity and a risk factor for overt
hypothyroidism during pregnancy. However, TgAb positivity has less diagnostic
accuracy for hypothyroidism than TPOAb positivity. Furthermore, as compared to
(euthyroid) TPOAb positivity, it is less likely that (euthyroid) TgAb positivity is a
risk factor for miscarriage or preterm birth. For these reasons, there are more studies
available on TPOAb positivity, and TPOAb positivity remains the primary thyroid
antibody to be checked for etiological or prognostic purposes both in pregnant and
non-pregnant individuals. Some studies in non-pregnant individuals have suggested
that thyroid sonography can identify individuals with thyroid antibody negative
thyroid autoimmunity. However, the lack of data in the perinatal period limits
the usefulness of ultrasound for detecting thyroid autoimmunity. Moreover, if the
indication for a thyroid ultrasound is unclear, the risks of diagnosing thyroid nodules or
small (i.e., not clinically meaningful) thyroid cancers, which might result in additional
testing or treatment, is more likely to outweigh any benefits.
• There is no indication for routine perinatal TgAb measurements.
• If a woman is known to have isolated TgAb positivity or previous incidental signs
of thyroid autoimmunity on ultrasound when entering the perinatal period, it is
sensible to approach thyroid management similar to the recommendations for
TPOAb positive women.
• A small subgroup in which additional TgAb measurement could be considered for
the purpose of identifying an indication for preconception or gestational thyroid
function screening would be a euthyroid TPOAb negative woman with a high risk of
thyroid autoimmunity (for example: previous thyroiditis, concomitant autoimmune
disease, first degree relative with thyroid autoimmunity) and a high-normal TSH.
