ObjectiveTo study the association between AMH and time to pregnancy. While it has been hypothesized that serum anti-Müllerian hormone (AMH) levels may indicate the chance of conception, findings have been mixed. Given that any association is expected to be modest, and it is possible that previous studies have been underpowered, we investigated this relationship in the largest prospective cohort to date. DesignProspective time-to-pregnancy cohort study. Subjects3,150 US women who had been trying to conceive for less than 3 months and had purchased a Modern Fertility Hormone Test. ExposureWe developed a discrete time-to-event model utilizing a binomial complementary log-log error structure within a generalized additive modeling framework, adjusting for confounding factors such as age, BMI, parity, smoking status, PCOS, and others. Sensitivity analyses were performed in women with regular menstrual cycles (21-35 days), who did not report using fertility treatments, using alternate AMH categories (<0.7, 0.7-8.5, >8.5 ng/mL), and AMH as a continuous measure. Main Outcome MeasuresPrimary outcomes included cumulative conception probability within 12 cycles and relative fecundability per menstrual cycle. Conception was defined by a self-reported positive pregnancy test. ResultsParticipants contributed 7.21 ± 5.32 cycles, with 1,325 (42.1%) achieving a pregnancy. Women with low AMH (<1ng/mL, n=427) had a lower chance of natural conception (Adjusted Hazard Ratio (adjHR 0.77, 95%CI 0.64, 0.94, p=0.009) compared to women with a normal AMH (1 - 5.5ng/mL). There was no difference between high (5.5+ ng/ml) and normal AMH categories (adjHR 1.11, 95% CI 0.94, 1.31, p=0.2). The inclusion of AMH improved the model (net reclassification index 0.10 [ 0.06 - 0.14); P<0.001). The instantaneous probability of conception was highest in cycle 4 across all AMH categories: the probability of natural conception was 11.2% (95% CI 9.0, 14.0) for low AMH, 14.3% (95% CI 12.3, 16.5) for normal AMH, and 15.7% (95%CI 12.9, 19.0) for high AMH. In the regular cycles sensitivity analysis (n=1,791), the low AMH group had a lower chance of conception (adjHR 0.77 95% CI 0.61, 0.97, p = 0.028) in the low AMH group compared to normal AMH, and similarly in the continuous model (adjHR 0.90; 95% CI 0.85-0.95, p<0.0001). ConclusionLow AMH levels (<1 ng/ml) are independently associated with a modest but significant reduction in the chance of conception.