{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T10:15:53Z","timestamp":1788257753197,"version":"build-2803163510"},"reference-count":22,"publisher":"Bioscientifica","issue":"4","license":[{"start":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T00:00:00Z","timestamp":1786924800000},"content-version":"vor","delay-in-days":16,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"content-domain":{"domain":["journals.bioscientifica.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,8,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Objective<\/jats:title>\n                    <jats:p>Infertility is a major health issue, and fertility treatments, including frozen embryo transfer (FET), are common. Progesterone, essential for endometrium development and receptivity, is used to improve implantation rates. This study investigates the effect of luteal phase support with progesterone on thyroid function in modified natural FET cycles.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>This is a sub-study of a randomized controlled trial (FET optimizing trial). Data were collected at two fertility centers from January 2019 to October 2022. Euthyroid women receiving single frozen\u2013thawed embryo transfer in a modified natural cycle were included. The study participants were categorized into two groups: the luteal phase support (LPS) and the no LPS groups. The LPS group received vaginal progesterone 100 mg three times daily starting at day 4 after ovulation trigger with human chorionic gonadotropin (day 0). A pregnancy test was performed on day 16. Thyroid function was repeatedly measured. Linear mixed modeling was used to test the effect of progesterone on thyrotropin (TSH, primary outcome) and free thyroxine (fT4). Interaction with thyroid autoimmunity was tested.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>In total, 85 women were included: 45 received progesterone LPS and 40 did not. Participants were 34 \u00b1 4 years of age and had a BMI of 23 (IQR: 21; 26), and 25% were positive for thyroid autoimmunity. Serum progesterone increased with LPS, but TSH and fT4 levels were not affected by LPS. There was no interaction with thyroid autoimmunity. In the progesterone LPS group, 44% conceived compared with 55% in the no LPS group, P = 0.33.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Progesterone LPS does not affect thyroid function during the luteal phase.<\/jats:p>\n                    <jats:sec>\n                      <jats:title>Trial registration number<\/jats:title>\n                      <jats:p>This trial was registered with ClinicalTrials.gov (NCT03795220) and EudraCT (2018-002207-34) and was completed.<\/jats:p>\n                    <\/jats:sec>\n                  <\/jats:sec>","DOI":"10.1530\/etj-26-0099","type":"journal-article","created":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T10:23:35Z","timestamp":1786962215000},"update-policy":"https:\/\/doi.org\/10.1530\/crossmarkpolicy-17","source":"Crossref","is-referenced-by-count":0,"title":["Effect of luteal phase support with progesterone on thyroid function: a sub-study of the FET optimizing trial"],"prefix":"10.1530","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9681-7394","authenticated-orcid":true,"given":"Diana","family":"Grove-Laugesen","sequence":"first","affiliation":[{"name":"Department of Endocrinology and Internal Medicine, Aarhus University Hospital 1 ,","place":["Denmark"]},{"name":"Department of Clinical Medicine, Health, Aarhus University 2 , ,","place":["Aarhus, Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2119-0013","authenticated-orcid":true,"given":"Marte","family":"Saupstad","sequence":"additional","affiliation":[{"name":"Fertility Clinic, Department of Gynaecology, Fertility and Obstetrics, Copenhagen University Hospital \u2013 Rigshospitalet 3 , ,","place":["Copenhagen, Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7632-6299","authenticated-orcid":true,"given":"Anette Vestergaard","family":"Gabrielsen","sequence":"additional","affiliation":[{"name":"Department of Clinical Medicine, Health, Aarhus University 2 , ,","place":["Aarhus, Denmark"]},{"name":"University Clinic for Fertility, Horsens Regional Hospital 4 ,","place":["Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7201-1268","authenticated-orcid":true,"given":"Eva","family":"Ebbeh\u00f8j","sequence":"additional","affiliation":[{"name":"Department of Endocrinology and Internal Medicine, Aarhus University Hospital 1 ,","place":["Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4308-3171","authenticated-orcid":true,"given":"Kristine","family":"L\u00f8ssl","sequence":"additional","affiliation":[{"name":"Fertility Clinic, Department of Gynaecology, Fertility and Obstetrics, Copenhagen University Hospital \u2013 Rigshospitalet 3 , ,","place":["Copenhagen, Denmark"]},{"name":"University Clinic for Fertility, Horsens Regional Hospital 4 ,","place":["Denmark"]},{"name":"Department of Clinical Medicine, University of Copenhagen 5 , ,","place":["Copenhagen, Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0589-021X","authenticated-orcid":true,"given":"Ulla Breth","family":"Knudsen","sequence":"additional","affiliation":[{"name":"Department of Clinical Medicine, Health, Aarhus University 2 , ,","place":["Aarhus, Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8340-104X","authenticated-orcid":true,"given":"Anja","family":"Pinborg","sequence":"additional","affiliation":[{"name":"Fertility Clinic, Department of Gynaecology, Fertility and Obstetrics, Copenhagen University Hospital \u2013 Rigshospitalet 3 , ,","place":["Copenhagen, Denmark"]},{"name":"Department of Clinical Medicine, University of Copenhagen 5 , ,","place":["Copenhagen, Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"416","published-online":{"date-parts":[[2026,8,17]]},"reference":[{"key":"2026090105414868600_bib1","doi-asserted-by":"crossref","first-page":"702","DOI":"10.1210\/er.2009-0041","article-title":"Thyroid function and human reproductive health","volume":"31","author":"Krassas","year":"2010","journal-title":"Endocr Rev"},{"key":"2026090105414868600_bib2","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1038\/s41574-023-00921-5","article-title":"Luteal phase support in assisted reproductive technology","volume":"20","author":"Garg","year":"2024","journal-title":"Nat Rev Endocrinol"},{"key":"2026090105414868600_bib3","doi-asserted-by":"crossref","first-page":"1061","DOI":"10.1016\/0002-9378(72)90181-0","article-title":"The significance of the human corpus luteum in pregnancy maintenance. 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