The “ue3” is the concentration of free estriol in the pregnant woman’s body. An important part of the Down’s syndrome screening test, which is performed in the middle of pregnancy to check for the risk of Down’s syndrome, is the measurement of free estriol. After the third trimester, the free estriol concentration is mainly secreted by the placenta and increases with the number of weeks of pregnancy. The concentration of free estriol decreases until just before full-term delivery. In cases of fetal malformations or placental dysfunction, the concentration of free estriol in the pregnant woman decreases significantly. The free estriol concentration in the pregnant woman’s blood can be measured during pregnancy to determine whether the placenta is functioning properly. The combination of free estriol, alpha-fetoprotein, and chorionic gonadotropin can be used to screen for Down’s syndrome.