{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T11:00:09Z","timestamp":1785150009804,"version":"3.55.0"},"reference-count":18,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T00:00:00Z","timestamp":1785110400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Clin. Med.","JCM"],"abstract":"<jats:p>Background\/Objectives: Letrozole combined with intrauterine insemination (IUI) is a common first-line treatment for unexplained and anovulatory infertility; however, the optimal dominant follicle size at human chorionic gonadotrophin (hCG) triggering remains uncertain. We evaluated associations of follicle size with biochemical pregnancy, clinical pregnancy, and live birth. Methods: This retrospective cohort included 596 letrozole\u2013IUI cycles from 454 women aged &lt;40 years treated between May 2024 and August 2025. Cycles were grouped by dominant follicle diameter at trigger (17.0\u201318.9, 19.0\u201321.0, and &gt;21.0 mm). Mixed-effects logistic regression accounted for repeated cycles. Results: Biochemical pregnancy, clinical pregnancy, and live-birth rates differed across groups and were highest at 19.0\u201321.0 mm; live-birth rates were 3.4%, 15.1%, and 8.6%, respectively (p = 0.008). Compared with 17.0\u201318.9 mm, the 19.0\u201321.0 mm group had higher adjusted odds of clinical pregnancy (aOR 5.58, 95% CI 1.31\u201323.84; p = 0.020) and live birth (aOR 15.15, 95% CI 1.74\u2013131.95; p = 0.014), although both estimates were imprecise. Adjusted live-birth probabilities were 3.5%, 16.1%, and 9.1%, respectively. The direction of the live-birth association was preserved in the single-cycle sensitivity analysis (aOR 3.85, 95% CI 1.22\u201312.13; p = 0.021). Continuous linear and quadratic follicle-diameter models were not significant. Conclusions: The 19.0\u201321.0 mm category was associated with higher reproductive outcome rates, including live birth; however, the observational design, sparse events, wide confidence intervals, and null continuous analyses preclude defining an optimal trigger threshold. These findings are hypothesis-generating and require prospective multicenter confirmation.<\/jats:p>","DOI":"10.3390\/jcm15155857","type":"journal-article","created":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T09:47:41Z","timestamp":1785145661000},"page":"5857","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Dominant Follicle Size as a Predictor of Pregnancy in Letrozole Intrauterine Insemination"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-9313-5250","authenticated-orcid":false,"given":"Emel","family":"\u00d6zalp","sequence":"first","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Belgin","family":"Savran \u00dc\u00e7ok","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"T\u00fcrkan","family":"Dikici Akta\u015f","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6570-1006","authenticated-orcid":false,"given":"Recep Taha","family":"A\u011fao\u011flu","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"\u00d6zg\u00fcr Volkan","family":"Akbulut","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-1881-1170","authenticated-orcid":false,"given":"Kubilay","family":"\u00c7anga","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"\u0130nci","family":"Kahyao\u011flu","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Ministry of Health, Ankara Etlik City Hospital, 06170 Ankara, Turkey"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"393","DOI":"10.1016\/j.fertnstert.2017.06.005","article-title":"The International Glossary on Infertility and Fertility Care, 2017","volume":"108","author":"Adamson","year":"2017","journal-title":"Fertil. 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