Category: Thyroid

Monitor: 32


Thursday, Apr 25
12:30 PM – 1:00 PM

Objective :

In women first diagnosed with hypothyroidism in pregnancy, The American thyroid association (ATA) task force recommends starting a fixed dose of 50 mcg while other experts dose based on the patient’s weight. The primary goal of this study is to compare the two most common methods of dosing levothyroxine in the context of pregnancy.

Methods :

This is a retrospective cohort study of women diagnosed and treated for hypothyroidism during pregnancy. Consecutive medical charts of women with the diagnosis of hypothyroidism in pregnancy followed at the pregnancy clinic of two Toronto academic hospitals between 2015-2017 were identified. Patients were divided into two groups based on the method used to initiate levothyroxine: A fixed dose group of patients who were started on 50 mcg of levothyroxine and a weight-based group of patients started on a dose based on the woman’s pre-pregnancy weight (1.35 mcg x pre-pregnancy weight) .The primary outcome was the percentage of patients who were at target (TSH<2.5) at the first follow-up visit, 4-8 weeks after initiating levothyroxine therapy. Sub-group analyses included: women who weighed more than 70 kg and women with positive TPO antibodies. A sensitivity analysis was done assessing those who were treated according to current 2017 ATA guidelines. A Chi squared test was used to compare percentages in both groups<./p>

Results :

354 records were reviewed. Of these, 68 women were excluded because the dosing method didn’t match either method or they were started on treatment in their third trimester of pregnancy.171 women received a fixed dose of levothyroxine and 115 women were dosed based on their weight. 155 (90.6%) of the women in the fixed group and 101(87.8%) of the women in the weight-based group were at target at first follow up (p=0.571). 24(11.8%) and 8(6.6%) women were over-treated (TSH<0.2) in the fixed and the weight based groups respectively (p=0.181). In the sub-group analysis of women who showed anti-TPO positivity, 90% of those in the weight-based group were at target at first follow up visit compared to 65% of those given a fixed dose of levothyroxine (p=0.0221).

Discussion :

In women with TPO Ab positivity, women in the weight-based group were more likely to achieve their target by the first visit following initiation of thyroxine than women in the fixed dose group. This was achieved with no significant increase in over-replacement.

Conclusion :

Women with hypothyroidism during pregnancy who are TPO Ab positive are more likely to reach their TSH target within the first 4-8 weeks after starting levothyroxine using a weight-based method compared to using a fixed low dose of levothyroxine.


Balsam Saeed Bohlega

endocrine fellow
University of Toronto
Toronto, Canada

I am a Thyroid fellow at the university of Toronto

Shoba Sujana Kumar

Assistant Professor of Medicine
University of Toronto
Toronto, Ontario, Canada

Assistant Professor of Medicine, University of Toronto. Division of Endocrinology & Metabolism, Department of Medicine Women's College Hospital
76 Grenville Street, Room 3416, Toronto, ON M5S 1B2

Afshan Zahedi

Associate Professor of Medicine
University of Toronto
Toronto, Ontario, Canada

After completing a degree in Biomedical Engineering in Ohio, USA, Dr. Zahedi graduated from University of Toronto, Faculty of Medicine and completed internal medicine residency and endocrinology fellowship at University of Toronto. Currently, she is an Associate Professor of Medicine at University of Toronto, Endocrinologist and Medical Director of the Thyroid program at Women’s College Hospital and Staff Endocrinologist at the Scarborough Health Network. Her research interest include: education, endocrine disorders in pregnancy and thyroid cancer.

George Tomlinson

Senior Scientist
Toronto General Hospital Research Institute

Department Of Medicine,Biostatistics Division ,Toronto General Hospital
Eaton North, 13th Fl. - Rm. 238, 200 Elizabeth Street,
Toronto, ON
M5G 2C4

Denice Feig

Associate Professor,
University of Toronto

Dr Denice Feig is an Associate Professor in the Division of Endocrinology and Metabolism at the University of Toronto, and holds a cross-appointment in both the Department of Obstetrics and Gynaecology and the Department of Health Policy, Management and Evaluation. She is Head of the Diabetes and Endocrine in Pregnancy Program at Mount Sinai Hospital, Chair of the University of Toronto Diabetes in Pregnancy Study Group and Past Chair of the Diabetes in Pregnancy Interest Group for the American Diabetes Association. She is a Senior Clinician Scientist at the Lunenfeld-Tananbaum Research Institute, an Adjunct Scientist at the Institute for Clinical and Evaluative Sciences and a Member of the Motherisk Team at SickKids Hospital. Her research focus is in the area of diabetes in pregnancy and she was recently awarded the Canadian Diabetes in Pregnancy Study Group Award for Excellence. She is the co-principal investigator of the CONCEPTT trial as well as principal investigator of the multi-centre, randomized trial, the MiTy trial and the MiTy Kids follow-up study. She has numerous peer-reviewed publications in the area of diabetes and thyroid disease in pregnancy.
Canada M5T 3L9