Timing luteal urinary pregnanediol glucuronide assessment using urinary luteinizing hormone: agreement with ultrasound-determined ovulation

Background Urinary pregnanediol glucuronide (PdG) is a non-invasive marker of luteal progesterone exposure, but its interpretation depends on timing relative to ovulation. We evaluated whether urinary luteinizing hormone (LH)-derived reference points could approximate ultrasound-determined ovulation (USDO) for scheduling mid-luteal PdG assessment. Methods This retrospective secondary analysis included 283 ultrasound-confirmed ovulatory cycles from 102 women. We evaluated the retrospectively identified urinary LH peak and the first urinary LH concentrations ≥10, ≥15, ≥20, ≥25, and ≥30 mIU/mL. PdG measured 6–9 days after each LH reference was compared with PdG measured on the corresponding USDO-timed day. A PdG threshold of ≥15 µg/mL was used for the primary descriptive classification, with sensitivity analyses at ≥5, ≥10, and ≥20 µg/mL. Ninety-five percent confidence intervals were estimated using participant-level cluster bootstrap. Results First urinary LH ≥15 mIU/mL occurred a median of 0 days from USDO (IQR −0.5 to +1), with 70.0% and 80.7% of events occurring within ±1 and ±2 days, respectively. At PdG ≥15 µg/mL, overall agreement ranged from 74.3% to 82.2% across days +6 to +9, with AUC values of 0.764–0.835. Alternative PdG thresholds produced different trade-offs between positive and negative agreement, while ≥15 µg/mL provided a comparatively balanced descriptive profile. Conclusions First urinary LH ≥15 mIU/mL is a candidate prospective reference for scheduling day-specific mid-luteal urinary PdG assessment. The present study establishes a candidate timing strategy rather than a clinically actionable decision rule; a single LH-timed PdG result should not be used alone to diagnose luteal dysfunction or direct treatment. These findings are hypothesis-generating; numerical LH and PdG thresholds are assay-dependent, require prospective platform-specific validation, and should not be interpreted as diagnostic criteria for luteal phase deficiency unless validated in a clinical trial.