OBJECTIVE: This study aimed to investigate the association between low basal total testosterone (TT) levels and the risk of recurrent pregnancy loss (RPL) in women with infertility. DESIGN: The study included women under 40 years with infertility, normal ovarian reserve, and regular ovulation. Participants were categorized into two groups: those with a history of recurrent pregnancy loss (RPL group) and those without a history of miscarriage (control group). All participants underwent in vitro fertilization (IVF) treatment. Serum TT and other sex hormone levels were measured on day 2 of spontaneous menstrual cycles and subsequently evaluated. Endocrine and coagulation conditions were also assessed. RESULTS: A total of 561 women were enrolled, into either the RPL group (n = 364) or the control group (n = 197) between January 2012 and December 2020. The RPL group demonstrated significantly lower median TT levels and were older compared with the control group (1.21 vs. 1.37 nmol/L, P = 0.001
34 vs. 33 years, P = 0.010). Additionally, fasting plasma insulin levels were higher in the RPL group (10.67 vs. 8.84 mU/L, P <
0.001). A negative correlation between basal TT levels and pregnancy loss frequency was observed. Low basal TT levels were significantly associated with RPL (OR: 1.58, 95 % CI: 1.04 - 2.41), with TT cut-off value of <
1.33 nmol/L indicating an increased likelihood of RPL (P <
0.001). CONCLUSION: Low basal serum TT levels are associated with an increased risk of RPL. However, further studies are required to evaluate the predictive value of basal TT levels in RPL risk.