Hypothyroidism
22
Box 3. Preconception and Gestational Considerations for the
Management of Hypothyroidism
Preconception
• Active assessment of a woman's desire to become pregnant and/or advising patients
to seek guidance for a future pregnancy will optimize preconception and gestational
management of hypothyroidism.
• If levothyroxine treatment establishes biochemical euthyroidism, the chance of
conception is optimized and the risk of adverse fertility/pregnancy outcomes is
similar to women without hypothyroidism.
• If treated with levothyroxine, a preconception TSH target of 0.5–2.5 mU/L can be used
to lower the risk of undertreatment during fertility treatments and/or early pregnancy.
• It is reasonable to temporarily increase the thyroid function testing frequency to once
every 3–6 months in women with treated hypothyroidism who are trying to conceive.
Gestational
• Most women will require a levothyroxine dose increase of approximately 25% by
week 12 and 50% by week 20, and the levothyroxine dose should thus be increased by
about 25% upon a positive pregnancy test considering the half-life of levothyroxine.
However, overtreatment with this approach is possible (see text).
• A typical monitoring strateg y in women with treated hypothyroidism would include
thyroid function testing every 4 weeks until midgestation and at least once near 30
weeks gestation.
Recommendations Table 9. Overt Hypothyroidism
Preconception and in Pregnancy
Strength
*
Level
#
For new onset maternal overt hypothyroidism during
pregnancy with a TSH less than 6 mU/L, confirmatory testing
may be performed within 3 weeks to verify an indication for
levothyroxine treatment.
Conditional Low
New onset maternal overt hypothyroidism during pregnancy
with a TSH equal or above 6 mU/L, or overt hypothyroidism
that persists aer retesting should be treated with levothyroxine.
Strong Moderate
Maternal hypothyroidism during pregnancy should be treated
with levothyroxine monotherapy. Other thyroid preparations
such as LT3 or desiccated thyroid should not be used in
pregnancy.
Strong Low
* Strength of Recommendation;
#
Level of Evidence; Good Practice Statement.
