Intermediate FMR1 cytosine‒guanine‒guanine repeats do not impair assisted reproductive technology outcomes in a large real-world cohort.
RESEARCH QUESTION: Does the presence of moderately elevated FMR1 cytosine‒guanine‒guanine (CGG) repeat numbers (40-70 repeats), identified through routine pre-pregnancy screening, adversely affect assisted reproductive technology (ART) outcomes in a real-world population? DESIGN: Retrospective cohort study including 760 first ART cycles conducted between 2010 and 2021 at a university-affiliated centre. FMR1 CGG repeat testing was conducted independently of infertility evaluation. Patients were categorized by repeat status in both alleles using two thresholds: 40 or more repeats (primary analysis) and 34 or more repeats (secondary analysis). Ovarian reserve markers, stimulation characteristics, oocyte yield, embryologic outcomes, positive beta-HCG and live birth rates were compared across groups. RESULTS: Among 760 patients, 669 (88%) had no allele of 40 or more repeats, 85 (11%) had one allele of 40 or more repeats and six (0.8%) had two alleles of 40 or more repats. The maximum observed repeat length was 71. Baseline demographics and ovarian reserve markers were similar between groups. No differences were observed in ovarian response, oocyte yield, fertilization or embryo development by FMR1 repeat category. Pregnancy and live birth rates were comparable between controls and patients with one expanded allele. Although elevated pregnancy and live birth rates were observed in patients with two expanded alleles, this subgroup was small, limiting interpretation. Analyses using the 34 or more repeat threshold yielded similar findings. CONCLUSIONS: Moderately elevated FMR1 CGG repeat numbers are not associated with impaired ART outcomes. Standard ART protocols remain appropriate, and FMR1 repeat length alone should not guide treatment modification in the absence of clinical ovarian insufficiency.