Estriol (E3)
Also called: Estriol, E3, Unconjugated estriol, uE3, Oestriol
One of the three substances measured in the triple test during pregnancy. It has no single adult reference range and is read only as part of that calculation.
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What it measures
Estriol is a form of oestrogen. In pregnancy it is measured as one of three components of the triple test: alongside alpha-fetoprotein, the test looks at human chorionic gonadotropin (hCG) and estriol in the mother's blood.
The triple test has two stated purposes: to examine whether there is a risk of open neural-tube defects in the developing fetus, and to assess the likelihood of Down syndrome. Estriol on its own answers neither question — it is one input to a calculation that also uses the week of pregnancy and the other two results.
Typical reference ranges
There is no single adult reference range for estriol, and that is not a gap in our data: the figure is interpreted against the week of pregnancy and combined with the other two triple-test results, rather than compared with a fixed band.
Your report will carry whatever the laboratory uses — often a multiple-of-the-median value rather than a raw concentration. The unit conversion below is simply arithmetic and says nothing about whether a value is expected.
What a high value can mean
What a low value can mean
Symptoms to look out for
None. Estriol is measured as part of a screening calculation, not because of a symptom, and the result is not something a person feels.
A triple test is offered routinely in pregnancy; being offered it does not imply that anything is wrong.
Many out-of-range results cause no symptoms at all - this is context, not a diagnosis.
When to discuss with a doctor
This result is not read on its own, and we do not interpret it here. An estriol figure means something only inside the triple-test calculation, together with the week of pregnancy and the other two measurements — and that calculation belongs with the doctor or midwife who ordered the test. If you are holding a triple-test report, bring it to whoever is following your pregnancy. They have the gestational dating the calculation depends on, and we do not.