E1G Levels After Embryo Implantation
After embryo implantation, urinary estrone-3-glucuronide (E1G) levels remain elevated and continue to increase, not drop. This persistent elevation is driven by the developing pregnancy, specifically by the corpus luteum under stimulation from human chorionic gonadotropin (hCG) produced by the implanting embryo.
Normal E1G Pattern in Ovulatory Cycles
- E1G rises during the follicular phase, beginning approximately 3-6 days before the LH surge, reflecting growing follicular activity 1, 2, 3
- Peak E1G levels occur 0.5 days prior to ovulation on average, with the peak closely clustered around the day of the LH surge 2, 3
- A persistent rise in E1G is observed from approximately 3 days pre-ovulation until 5 days post-ovulation, demonstrating that E1G does not immediately drop after ovulation 2
- E1G levels remain elevated during the luteal phase in ovulatory cycles, showing a 5-7 fold increase from early follicular phase baseline to peak/luteal levels 1, 4
E1G Pattern After Implantation
- When pregnancy occurs, E1G levels continue to rise rather than declining, as the corpus luteum remains active under hCG stimulation from the implanting embryo 4, 2
- The continued elevation of E1G post-implantation is part of the normal hormonal support for early pregnancy, with estrogen production maintained by the corpus luteum until the placenta assumes this function 5
- During pregnancy, estradiol (the parent hormone of E1G) increases approximately 50-fold compared to pre-pregnancy levels, confirming the massive elevation in estrogen production that would be reflected in urinary E1G 5
Clinical Interpretation for Fertility Tracking
- A sustained rise in E1G (calculated as a significant cumulative sum) provides the best index for predicting ovulation, typically occurring 3-6 days before the LH surge 1, 3
- The ratio of E1G to creatinine in morning urine gives the most compact distribution of sustained rises, making it the preferred measurement for fertility monitoring 1
- Post-ovulatory monitoring requires assessment of pregnanediol-3-glucuronide (PdG) rather than E1G alone, as PdG rises after ovulation and provides evidence of corpus luteum function 4, 6, 2
- In conception cycles, both E1G and PdG remain elevated, with PdG peaking approximately 7.5 days after ovulation and remaining high to support early pregnancy 2, 3
Common Pitfall to Avoid
Do not expect E1G to drop after implantation—this would indicate pregnancy failure or corpus luteum insufficiency 4, 2. The hallmark of successful implantation is sustained elevation of both estrogen metabolites (E1G) and progesterone metabolites (PdG), driven by hCG production from the developing embryo 5, 2.