This test measures the level of Estriol in the blood. Estriol (E3) is one of the 3 main

components of Estrogen along with Estradiol and Estrone. During pregnancy, estriol is

produced by the placenta.ncreasing levels are an indication of the health of the pregnancy

and developing baby. Estriol is part of the second trimester maternal serum screen, a test

performed to evaluate fetal risk due to certain chromosomal abnormalities. Very low levels

of E3 are present in non- pregnant women or men.