Is levothyroxine safe in pregnancy
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Safety of Levothyroxine in Pregnancy
Introduction to Levothyroxine and Pregnancy
Levothyroxine (LT4) is a synthetic form of the thyroid hormone thyroxine, commonly prescribed to manage hypothyroidism. Its use during pregnancy, particularly in women with subclinical hypothyroidism (SCH) or thyroid autoimmunity (TAI), has been the subject of extensive research due to potential implications for maternal and fetal health.
Levothyroxine and Subclinical Hypothyroidism in Pregnancy
Benefits in Assisted Reproduction Technologies (ART)
Research indicates that LT4 supplementation can significantly improve pregnancy outcomes in women with subclinical hypothyroidism undergoing assisted reproduction technologies (ART). A meta-analysis found that LT4 treatment resulted in a higher delivery rate and a lower miscarriage rate among these women . However, the effect on clinical pregnancy rates was not significant .
General Pregnancy Outcomes
For pregnant women with SCH, LT4 treatment has been associated with a reduced risk of pregnancy loss, preterm birth, and gestational hypertension. A systematic review and meta-analysis highlighted that LT4 supplementation in pregnant women diagnosed with SCH based on recent diagnostic criteria significantly lowered the risks of these adverse outcomes . Another meta-analysis confirmed the beneficial effects of LT4 in reducing pregnancy loss and preterm birth among women with SCH and/or TAI .
Levothyroxine and Thyroid Autoimmunity in Pregnancy
Impact on Live Birth Rates
The impact of LT4 on live birth rates in women with thyroid autoimmunity has been mixed. Some studies have shown no significant improvement in live birth rates with LT4 supplementation in euthyroid women with thyroid peroxidase antibodies (TPO-Ab) Wang2020Dhillon-Smith2019Lau2021. For instance, a large double-blind, placebo-controlled trial found no significant difference in live birth rates between the LT4 and placebo groups .
Miscarriage and Preterm Birth
While LT4 treatment has not consistently improved live birth rates, it has shown potential in reducing miscarriage rates. A meta-analysis found that LT4 supplementation significantly decreased the miscarriage rate in women with SCH and/or TAI undergoing in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) . However, the same study noted no significant effect on preterm birth rates .
Safety and Adverse Events
The safety profile of LT4 during pregnancy has been generally favorable. Most studies report no significant increase in adverse events with LT4 treatment compared to placebo Dhillon-Smith2019Van Dijk2022. However, one study noted a slightly higher incidence of serious adverse events in the LT4 group, though this was not statistically significant .
Conclusion
In summary, LT4 supplementation appears to be beneficial in reducing miscarriage rates and improving certain pregnancy outcomes in women with subclinical hypothyroidism and/or thyroid autoimmunity. However, its impact on live birth rates remains inconclusive, particularly in euthyroid women with thyroid autoimmunity. The safety profile of LT4 during pregnancy is generally acceptable, with no significant increase in adverse events reported. Further research is needed to fully understand the benefits and risks of LT4 supplementation in different subgroups of pregnant women.
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