Estriol, Free (FE3), Serum


Estriol is an oestrogen derived from the placental aromatization of foetal adrenal androgens. Along with two other pregnancy-associated parameters, estriol is used during the second trimester to evaluate the risk of having Down’s syndrome and open neural tube defect. By the seventh week of gestation, the production of these adrenal androgens is controlled by pituitary ACTH stimulation; therefore, low levels of foetal adrenal androgens caused by primary or secondary adrenal insufficiency can lead to low maternal estriol levels. Serum free estriol is a more useful and up-to-the-minute indicator than total estriol, due to its short half-life in the maternal circulation.


Low free estriol level, is usually correlated with compromised uteroplacental perfusion and frequently associated with foetal death. The most common genetic cause of extremely low estriol levels is steroid sulfatase deficiency, the prenatal manifestation of X-linked recessive ichthyosis (widespread scaling of the skin). Other rare causes of low maternal estriol include Smith-Lemli-Opitz syndrome caused by a defect in the final step of cholesterol biosynthesis and associated with congenital anomalies, microcephaly, and intrauterine growth retardation. Maternal estriol is also decreased in Isolated Adrenocorticotropic Hormone Deficiency. This test is used as a parameter of the second trimester maternal screen.

Sample Type, Quantity & Conditions

1 ml Serum Stability: 7 Days at 2-8 °C

Special Precautions

State date of LMP. Avoid grossly haemolysed or grossly lipemic samples.

Normal Range

By Report

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