Estriol test in pregnancy: free estriol (uE3)

Free estriol (unconjugated estriol, uE3) is an estrogen-type hormone that during pregnancy is made jointly by the placenta and the fetal liver and adrenal glands. Unlike other estrogens, the production of estriol requires a functioning fetal organism, which is why its level in the blood is considered one of the indicators reflecting the state of the placenta and the fetus. According to MedlinePlus, free estriol is measured as one of four markers in the second-trimester screening test called the “quad screen”, or the four-marker test (quadruple screen), together with alpha-fetoprotein (AFP), chorionic gonadotropin (hCG) and inhibin A. This test is carried out at 15–22 weeks of pregnancy and helps assess the risk of certain fetal developmental disorders, but on its own it does not confirm a diagnosis — an unusual result is grounds for further, more precise tests.

• During second-trimester pregnancy screening (at 15–22 weeks of pregnancy), as part of the so-called “quad screen” together with AFP, hCG and inhibin A
• When the risk of fetal chromosomal disorders is to be assessed, for example Down syndrome or Edwards syndrome
• When the risk of spinal cord and brain developmental defects is to be assessed additionally, together with the AFP marker
• When the doctor, taking into account the pregnant woman’s age or other risk factors, recommends extended prenatal screening

No single numeric range is given here — the exact numeric interval is given by the laboratory. An unusual level of the marker, together with the other markers, can point to a greater risk of fetal developmental disorders, and the result is assessed taking the duration of the pregnancy into account.

A low free estriol

A low free estriol, assessed together with the other “quad screen” markers, does not establish a diagnosis on its own. According to MedlinePlus, lower AFP and estriol together with higher hCG and inhibin A levels can point to a greater risk of conditions such as Down syndrome. Such a result is grounds for discussing further, more precise tests with a doctor.

What a low result can be linked to

• Together with the other markers (a lower AFP, higher hCG and inhibin A) — a greater calculated risk of Down syndrome
• Certain chromosomal disorders, for example Edwards syndrome
• An inaccurately determined stage of pregnancy — screening markers are assessed according to the week of pregnancy, so a wrongly calculated duration can distort the result

What to discuss with a doctor

• The result is always assessed together with AFP, hCG and inhibin A, not on its own
• A more precise clarification of the stage of pregnancy by ultrasound, if there is doubt about the result
• A discussion with a doctor about whether additional, more precise tests are needed (for example a cell-free fetal DNA test (cfDNA) or a consultation with a geneticist)
• This test shows a calculated risk — on its own it neither confirms nor rules out a fetal disorder

Related pages: AFP, hCG, beta-hCG, estradiol, progesterone and tests during pregnancy.