Updated June 04, 2014.

According to a study reported on in the Journal of Clinical Endocrinology and Metabolism, when a woman being treated for hypothyroidism becomes pregnant, she should immediately increase her levothyroxine dose by two tablets per week, in order to maintain her thyroid function in the normal ("euthyroid") range. According to the study, the addition of two additional dosages per week can significantly reduces the risk of hypothyroidism in the mother.

(Maternal hypothyroidism in early pregnancy is associated with an increased risk of miscarriage, and in developmental and cognitive delays and deficiencies in children.)

In this study, the women began increasing their dosage at around 5 1/2 weeks of pregnancy. Interestingly, at that early point, 27% of the study participants already had a TSH level elevated above 5.0, indicative of hypothyroidism.

A subset of the women did end up getting too much thyroid medication, and required further adjustment. The researchers suggest that those who are more likely to end up slightly overdosed include women without a thyroid, those whose TSH level prior to pregnancy was less than 1.5, and those who are taking at least 100 mcg/day of levothyroxine prior to pregnancy.

The study emphasized the importance of early pregnancy detection and action on the part of the patients, writing: "In clinical practice, women do not typically seek obstetrical care before 8-12 weeks gestation. Thus, patients themselves must understand the importance of initial (levothyroxine) adjustment immediately upon a missed menstrual cycle and a positive home pregnancy test."

According to the researchers, increasing the levothyroxine dosage by approximately 30% -- two extra dosages weekly -- as soon as pregnancy is confirmed "significantly reduces the risk of maternal hypothyroidism throughout the first trimester. Monitoring thyroid function approximately once monthly is required through midpregnancy because a minority of patients may require subsequent L-T4 dose modifications to maintain appropriate TSH concentrations."
More Information on Thyroid Disease in Pregnancy

• Managing Thyroid Disease During and After Pregnancy: Guidelines
• Fertility, Infertility, Pregnancy & Thyroid Disease Information Center
• Pregnant with Hypothyroidism? Increase Your Medication!!!
• What Are The Normal TSH Ranges During Each Trimester of Pregnancy?
• Hypothyroidism and PregnancyGuidelines for Thyroid Disease & Pregnancy: American Thyroid Association Issues Guidelines for Pregnant Women

_{Source: Leila Yassa, Ellen Marqusee, Rachael Fawcett, and Erik K. Alexander. "Thyroid Hormone Early Adjustment in Pregnancy (The THERAPY) Trial." Journal of Clinical Endocrinology & Metabolism. Published online: May 12, 2010.} About Mary Shomon | Thyroid Forum | Twitter | Facebook
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