What this test measures
Estriol (E3) is the dominant oestrogen of pregnancy. Production requires intact contributions from the foetal adrenal glands, foetal liver, and placenta — making maternal serum estriol a single marker that reflects the integrated function of the foeto-placental unit. "Unconjugated" estriol is the active fraction not yet bound to sulphate / glucuronide; this is what is measured (rather than total estriol).
Unconjugated estriol rises steadily through pregnancy. In trisomy 21 and trisomy 18, uE3 is lower than expected for gestational age — typically 0.7–0.8 MoM in trisomy 21 and below 0.5 MoM in trisomy 18. uE3 is therefore included as one of three markers in the Triple Marker test and one of four in the Quadruple Marker test, both done between 15 and 22 weeks of gestation.
Why it matters
Unconjugated estriol is rarely ordered alone outside aneuploidy screening because its diagnostic value comes from being combined with AFP, β-hCG, and (for Quad) Inhibin A. Very low uE3 (<0.15 MoM) in isolation is a red flag for rare metabolic and adrenal conditions — Smith-Lemli-Opitz syndrome, placental sulfatase deficiency, foetal adrenal insufficiency, and steroid sulphatase deficiency (X-linked ichthyosis) — and an undetectable uE3 always warrants foetal medicine review.
For Indian patients, the test reaches the patient as a Triple or Quadruple Marker risk number — the individual uE3 MoM is on the report but interpreted alongside the other markers.
How to prepare
No fasting required. Schedule between 15+0 and 22+0 weeks gestation. Bring accurate gestational age (LMP or dating scan); MoM is calculated against the expected level for that exact day of pregnancy.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Unconjugated Estriol (uE3) (ng/mL (or MoM))[1][2] | Median MoM = 1.0 (range 0.5–2.0 typical) | Mildly low MoM (0.7–0.8) — associated with trisomy 21. Low MoM (<0.5) — associated with trisomy 18. Very low or undetectable uE3 (<0.15 MoM) — flag for rare metabolic conditions (Smith-Lemli-Opitz syndrome, X-linked ichthyosis, foetal adrenal insufficiency, placental sulfatase deficiency). Foetal medicine review needed. | High uE3 is not typically associated with chromosomal abnormality. May occasionally reflect wrong gestational dating (sample taken later than recorded). |
uE3 patterns and what they suggest
| uE3 MoM | Likely condition | Recommended action |
|---|---|---|
| 0.5 – 2.0 | Normal | Routine antenatal care |
| 0.7 – 0.8 | Possible trisomy 21 (if combined markers also suggest) | Combined Quad risk + counselling |
| < 0.5 | Possible trisomy 18 | NIPT / amniocentesis |
| < 0.15 (very low) | Rare conditions (SLOS, sulfatase deficiency) | Foetal medicine review + further metabolic workup |
Frequently asked questions
What is unconjugated estriol?
It is an oestrogen made by the developing baby (foetal adrenal glands and liver) and the placenta. Its level in maternal blood reflects the joint function of the foeto-placental unit and is used in second-trimester aneuploidy screening.
When is it tested?
Between 15+0 and 22+0 weeks, as part of the Triple Marker or Quadruple Marker tests.
Is uE3 ordered alone?
Rarely. Its value comes from combination with AFP, β-hCG, and Inhibin A. A stand-alone uE3 may be ordered to investigate a very specific concern (e.g. suspected Smith-Lemli-Opitz syndrome).
Do I need to fast?
No.
My uE3 is 0.6 MoM — what does that mean?
0.6 MoM is on the lower side. By itself it is not diagnostic. The Triple/Quad risk number — which combines uE3 with the other markers, your age, and gestational age — is what your doctor will use to decide next steps.
What does an undetectable uE3 mean?
Very low or undetectable uE3 (<0.15 MoM) is rare and is a flag for unusual conditions such as Smith-Lemli-Opitz syndrome, X-linked ichthyosis (placental sulfatase deficiency), or foetal adrenal insufficiency. Foetal medicine referral is needed for further evaluation.
Does uE3 also predict pre-eclampsia?
Persistently low uE3 reflects placental dysfunction and has been linked to adverse outcomes (IUGR, pre-eclampsia, preterm birth) but it is not used as a stand-alone predictor in routine practice.
Why does it matter to have an accurate LMP?
uE3 rises rapidly week by week. Incorrect gestational age throws off the MoM and can produce a falsely abnormal result. A dating scan is preferred to LMP when there is doubt.
Related Pregnancy / Prenatal tests
Tests commonly ordered alongside UNCONJUGATED ESTRIOL (E3), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Second Trimester Screening · accessed 2026-05-30T00:00:00.000Z
- ACOG — Screening for Fetal Chromosomal Abnormalities · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Estriol · accessed 2026-05-30T00:00:00.000Z
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