For the millions of women undergoing fertility treatment, the assumption that more medication means better outcomes is increasingly being challenged. A large national analysis now suggests that cumulative exposure to clomiphene citrate during IVF ovarian stimulation may carry measurable reproductive risks that scale with dose — a finding with real implications for how fertility clinics calibrate protocols.
Drawing on nearly two decades of US fertility clinic data (2004–2021), this retrospective cohort study analyzed 21,004 fresh autologous embryo transfer cycles in which clomiphene citrate (CC) was used for ovarian induction. Cycles were stratified into four cumulative dose categories: under 500 mg, 500–749 mg, 750–999 mg, and 1,000 mg or above. Using robust Poisson regression with adjustment for confounders, researchers found that spontaneous abortion rates rose progressively with dose — from 10.3% in the lowest-dose group to 11.8% (adjusted risk ratio 1.12) and 14.4% (aRR 1.38) in the two middle tiers. The highest-dose group showed an approximately threefold elevated stillbirth rate compared with the sub-500 mg reference group, though precision around that estimate was limited, likely due to small numbers at that dosing extreme.
Clomiphene citrate has been a cornerstone of ovarian stimulation since the 1960s, but its pharmacodynamics — particularly its anti-estrogenic effects on endometrial receptivity — have long raised questions about uterine environment quality at higher cumulative exposures. This study adds population-level observational weight to those mechanistic concerns. The dose-response gradient seen here is biologically plausible: prolonged anti-estrogenic signaling could impair implantation quality or placental development in ways that compound with dose. However, critical limitations apply. As a retrospective observational design, unmeasured confounding by indication — where clinicians may escalate dosing precisely because patients have poorer baseline prognosis — cannot be excluded. The stillbirth finding in the highest-dose tier also rests on a small subgroup (3.7% of cycles), warranting cautious interpretation. Nonetheless, the scale of the dataset and the consistent gradient across miscarriage endpoints make this an incremental but meaningfully informative addition to fertility medicine's evidence base.