Levothyroxine use during pregnancy
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Levothyroxine Use During Pregnancy: Effects on Hypothyroidism and Pregnancy Outcomes
Levothyroxine for Overt and Subclinical Hypothyroidism in Pregnancy
Levothyroxine is the standard treatment for overt hypothyroidism during pregnancy, and its use is strongly supported by guidelines to reduce the risk of adverse outcomes such as miscarriage and to maintain maternal thyroid-stimulating hormone (TSH) below 2.5 μIU/mL . For subclinical hypothyroidism (SCH), where TSH is elevated but free thyroxine (FT4) is normal, the evidence is less clear. However, several meta-analyses and systematic reviews indicate that levothyroxine treatment in pregnant women with SCH can reduce the risk of pregnancy loss and neonatal death Bein2021Provinciatto2024. The benefit appears to be more pronounced when TSH levels are above 4.0 mU/L .
Impact on Pregnancy Loss, Preterm Birth, and Neonatal Outcomes
Multiple studies show that levothyroxine therapy in women with SCH during pregnancy is associated with a lower risk of pregnancy loss, including miscarriage and stillbirth Bein2021Grandi2023Provinciatto2024. In women undergoing assisted reproduction technologies (ART), levothyroxine supplementation has been shown to significantly increase delivery rates and reduce miscarriage rates . However, the effect on live birth rates in the general population is less clear, with some studies finding no significant improvement Provinciatto2024Sankoda2024.
Regarding preterm birth, the evidence is mixed. Some studies suggest that levothyroxine may reduce the risk of preterm birth in women with SCH and TSH levels above 4.0 mU/L, but not in those with lower TSH levels . Conversely, one large cohort study found an increased risk of preterm birth in children born to mothers treated with levothyroxine during pregnancy, though this may be confounded by the underlying thyroid disease itself .
Neurodevelopmental and Childhood Outcomes
Current research does not show a significant association between maternal levothyroxine use during pregnancy and neurodevelopmental outcomes such as attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder (ASD) in offspring Bein2021Ge2022. Similarly, no differences have been observed in cognitive status in children at 3 or 5 years of age following maternal levothyroxine treatment for SCH .
Levothyroxine Use in Women with Thyroid Autoimmunity
For women with thyroid autoimmunity but normal thyroid function, levothyroxine treatment does not appear to improve pregnancy rates, reduce miscarriage, or lower the risk of preterm delivery or increase live births . Guidelines generally do not recommend levothyroxine for euthyroid women with thyroid autoimmunity Urgatz2024Lau2021.
Metabolic and Neonatal Health Considerations
Recent metabolomics research suggests that levothyroxine-treated pregnancies may show alterations in cord blood metabolites linked to fetal hypoxia and muscle degradation, which could affect newborn health as measured by Apgar scores . However, these findings are preliminary and require further investigation.
Practical Considerations and Research Gaps
While levothyroxine is clearly beneficial for overt hypothyroidism and for some women with SCH (especially with higher TSH levels), its use in other groups, such as those with thyroid autoimmunity or lower TSH elevations, is not supported by current evidence Urgatz2024Sankoda2024Man2025+1 MORE. There is also a need for more research to clarify the benefits and risks of levothyroxine in specific subgroups and to optimize thyroid care during pregnancy Urgatz2024Man2025.
Conclusion
Levothyroxine is essential for managing overt hypothyroidism in pregnancy and can reduce the risk of pregnancy loss in women with SCH, particularly when TSH is above 4.0 mU/L. Its benefits for other groups, such as women with thyroid autoimmunity or lower TSH elevations, are not supported by current evidence. The impact on preterm birth and neonatal metabolic health remains uncertain, highlighting the need for individualized care and further research.
Sources and full results
Most relevant research papers on this topic
Levothyroxine and the risk of adverse pregnancy outcomes in women with subclinical hypothyroidism: a systematic review and meta-analysis
Levothyroxine treatment during pregnancy is associated with decreased risks of pregnancy loss and neonatal death in women with subclinical hypothyroidism.
Update on therapeutic use of levothyroxine for the management of hypothyroidism during pregnancy
Levothyroxine (LT4) treatment reduces the risk of adverse pregnancy outcomes in overt hypothyroidism during pregnancy, with subclinical hypothyroidism potentially reducing the chance of a successful pregnancy.
Levothyroxine initiation and the risk of pregnancy loss among pregnant women with subclinical hypothyroidism: An observational study emulating a target trial.
Initiation of levothyroxine during pregnancy is associated with a lower risk of pregnancy loss in women with subclinical hypothyroidism.
Levothyroxine treatment during pregnancy: a metabolomics study
Levothyroxine treatment during pregnancy may cause changes in umbilical cord serum metabolites linked to fetal hypoxia and muscle degradation, potentially impacting newborn health.
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