Abstract
OBJECTIVE: To study the association between previous use of levonorgestrel intrauterine system (LNG-IUS) and endometrial thickness (EMT) in women undergoing in vitro fertilisation (IVF)/intracytoplasmic sperm injection (ICSI) cycles. DESIGN: Multicentre historical cohort study. SETTING: Eight Danish public and private fertility clinics. POPULATION: 12786 women aged 18-46 years contributing with an EMT measurement from 22 464 different IVF/ICSI treatment cycles between 2000 and 2021. METHODS: Exposure was previous use of LNG-IUS, combined oral contraceptive pills (OCPs), progeste-only pills (POPs), no/other contraception or combined, cumulated use of contraception when more contraceptives had been used during the inclusion period. Further, ever use of LNG-IUS was categorised into 0-3 years, > 3-6 years, > 6-9 years and > 9 years. Mixed effect logistic regression adjusted for age, BMI, smoking, educational level, total FSH dose and fertility clinic was used. MAIN OUTCOME MEASURE (S): EMT (< 7 mm ≥ 7 mm). RESULTS: Statistically significantly higher odds of EMT ≥ 7 mm were found for OCPs [odds ratio (OR) 3.53 (95% confidence interval (95% CI) 1.29-9.65)], POPs [OR 6.43, (95% CI 1.45-28.63)] and no/other contraception [OR 6.67, (95% CI 2.37-18.74]) relative to LNG-IUS in IVF/ICSI cycles. Further, all duration categories of ever use of LNG-IUS were associated with statistically significantly lower odds of obtaining an EMT ≥ 7 mm compared to no/other contraception. CONCLUSIONS: In this study, previous use of LNG-IUS was associated with decreased endometrial growth in women undergoing IVF/ICSI.