THEoestriol(or estriol) is a ” serum marker »Used to assess the risk of Down’s syndrome in a fetus being pregnancy. More precisely, so-called unconjugated estriol (also noted uE3) is one of the second trimester serum markers, along with alpha-feotoprotein and beta-hCG.

These are measured in maternal blood between 14 weeks of amenorrhea (SA) and 17SA + 6 days.

Unconjugated estriol is secreted by the fetus and placenta. Its concentration reflects the synthesis and regulation of steroid hormones in the fetus.

The estriol level analysis is used for screening for Down’s syndrome.

In fact, the preferred examination is the ” combined screening »Of the first trimester, which combines the measurement of nuchal translucency by ultrasound (between 11 and 13 WA + 6 days) with maternal serum markers of the first trimester, which do not include estriol (they are composed of PAPP-A and free beta-HCG).

This screening is offered to all pregnant women in France (and in most hospitals in Quebec).

If this test could not be carried out, the pregnant woman can benefit from a screening of the second trimester, which relies in part on the dosage of estriol (in addition to that of alpha-feotoprotein and beta). hCG).

The assay is performed on a blood sample from the pregnant woman. The result is combined with ultrasound measurements of nuchal clarity and craniocaudal length that were performed in the first trimester. The other markers are assayed at the same time.

During a normal pregnancy, estriol levels rise sharply until term.

In pregnancies where the fetus has Down’s syndrome or other chromosomal abnormality, maternal unconjugated estriol levels are lower than normal (

This situation concerns about 0,25% of pregnant women. In this case, a specialized ultrasound will be advised, to ensure that the fetus does not have trisomy 21 or trisomy 18, for example.

Most often, combined screening does not detail the estriol level but gives an assessment of the overall risk of trisomy 21. If the risk is considered to be greater than 1/250, in France, the screening will be considered positive. The woman will then be offered an amniocentesis or a chorionic villus (or trophoblast) sample in order to perform the karyotype of the fetus and obtain a definite diagnosis.