E3G (Estrone-3-Glucuronide)

Hormones & Labs · Reviewed August 2026

Definition

E3G (estrone-3-glucuronide) is a breakdown product of estradiol that leaves the body in urine. The liver converts estradiol to estrone and attaches a glucuronide group so it can be excreted.[1] Urinary E3G rises and falls with serum estradiol, which is why at-home fertility monitors read it to follow the cycle's estrogen curve.[2]

Educational content, not medical advice. For personal or fertility concerns, please consult your doctor.

What E3G Measures

E3G isn't a hormone the ovaries make. It's what's left after the body processes estradiol, the main estrogen of the reproductive years. Estradiol converts to estrone as the body metabolizes it, and the liver conjugates estradiol's metabolites with glucuronic acid or sulfate on their way out.[1] Estradiol and its metabolites leave the body mostly through urine, in those conjugated forms.[1] E3G is one of them, the glucuronide of estrone.

Because E3G traces back to estradiol, the amount in urine moves with the amount of hormone in blood. A 2015 study tracked 40 women through a full cycle with daily urine and blood samples, referenced to ultrasound-confirmed ovulation, and found the urinary and serum hormone profiles showed excellent agreement.[2]

How It's Measured

E3G is measured from a urine sample, no blood draw needed. At-home fertility monitors read it, usually alongside urinary LH, and track how the level changes from day to day.[3] Daily blood draws aren't practical at home, and a daily urine test is.

Why People Track E3G

Estradiol climbs through the follicular phase as a follicle matures, and in the 2015 comparison study the rise in estrogen and LH always came before ovulation.[2] An LH surge arrives late in that build-up. Rising E3G shows up earlier. In one home-monitor study, E3G thresholds flagged the urinary LH peak up to five days in advance in 82.8% of cycles.[3] That's why monitors that read both hormones can mark high-fertility days before the surge itself.

For how these urine tests work more broadly, see our guide to at-home hormone tests.

How Go Go Gaia Tracks E3G

Go Go Gaia doesn't sell a monitor, but you can log or upload the E3G readings from the one you use. The app charts each value against your cycle day, right next to your urine LH results, so the estrogen rise and the LH surge sit on one timeline.

Put your monitor's E3G readings on your cycle chart

Log at-home hormone results and Go Go Gaia charts E3G and LH side by side, by cycle day.

Get Go Go Gaia

Free on the App Store.

What the Research Shows

The Roos study compared daily urinary and serum hormones referenced to ultrasound-confirmed ovulation and concluded the two may be used interchangeably for monitoring the cycle.[2]

Monitor readings hold up against clinical references too. In a 150-cycle home-use trial of a monitor reading urinary hormone levels, ovulation never occurred before the monitor's peak-fertility days.[4]

Serum still wins on precision. A 2024 comparison found serum estradiol signaled the start of the fertile window with greater accuracy and sensitivity than monitor E3G, with more fluctuation in the urinary readings.[5] Our estradiol entry covers that serum-versus-urine comparison in more detail.

Related Terms

Estradiol (E2)

The hormone E3G comes from, and what a serum panel measures directly.

Estrone (E1)

The estrogen that lends E3G its name, measured as a hormone in its own right.

LH Surge

The later urine signal monitors pair with E3G to narrow down ovulation.

PdG (Pregnanediol Glucuronide)

E3G's counterpart: the urinary metabolite of progesterone.

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

Is E3G the same as estradiol?

No. Estradiol is the hormone circulating in blood. E3G is what remains after the body converts estradiol to estrone and packages it for excretion in urine. Monitors read E3G because it moves with estradiol, not because it's the hormone itself.

Why do fertility monitors measure E3G instead of estradiol?

Measuring estradiol directly takes a blood draw, which isn't practical every day at home. E3G shows up in urine, so a monitor can read it daily without a needle. Because urinary E3G tracks serum estradiol closely, the urine reading stands in for the blood one.

What's the difference between E3G and PdG?

Both are urinary hormone metabolites that at-home monitors can read. E3G comes from estradiol, the estrogen that rises in the lead-up to ovulation. PdG comes from progesterone, the hormone of the luteal phase. Monitors use E3G for the early part of the cycle's hormone story and PdG for the later part.

References

  1. Delgado BJ, Patel P, Lopez-Ojeda W. Estrogen. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Updated August 9, 2025. ncbi.nlm.nih.gov/books/NBK538260
  2. Roos J, Johnson S, Weddell S, et al. Monitoring the menstrual cycle: Comparison of urinary and serum reproductive hormones referenced to true ovulation. Eur J Contracept Reprod Health Care. 2015;20(6):438-450. pubmed.ncbi.nlm.nih.gov/26018113
  3. Tanabe K, et al. Prediction of the potentially fertile period by urinary hormone measurements using a new home-use monitor: comparison with laboratory hormone analyses. Hum Reprod. 2001;16(8). pubmed.ncbi.nlm.nih.gov/11473952
  4. Behre HM, Kuhlage J, Gassner C, et al. Prediction of ovulation by urinary hormone measurements with the home use ClearPlan Fertility Monitor: comparison with transvaginal ultrasound scans and serum hormone measurements. Hum Reprod. 2000;15(12):2478. pubmed.ncbi.nlm.nih.gov/11098014
  5. Usala SJ, Vineyard DD, Kastis M, Trindade AA, Gill HS. Comparison of Day-Specific Serum LH, Estradiol, and Progesterone with Mira™ Monitor Urinary LH, Estrone-3-glucuronide, and Pregnanediol-3-glucuronide Levels in Ovulatory Cycles. Medicina (Kaunas). 2024;60(8):1207. pmc.ncbi.nlm.nih.gov/articles/PMC11356644

Sourced from peer-reviewed research and, for basic mechanism claims, established references like NIH and StatPearls. Every citation above is checked to confirm it resolves to a real source and supports the sentence it's attached to. Last reviewed August 2026. See our full methodology on the Encyclopedia hub.