Unconjugated Estriol (uE3)

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Estriol is a female sex hormone that increases during pregnancy. The hormone produced by the fetus and passed into the mother's bloodstream. Levels of this hormone can be tested via a blood test (quad screen) during the second trimester.
Estriol (also oestriol) is one of the three main estrogens produced by the human body. The hormonal functions of uE3, a relatively weak estrogen, are not well understood. During pregnancy, estrogens are thought to maintain proper functioning of the uterus, soften cervix and aid lactation. Maternal serum uE3 levels rise above non-pregnancy levels by 7-9 weeks gestation and continue to increase throughout pregnancy. Low levels of maternal uE3 in the third trimester have been reported in newborns with low birth weight and have been found to indicate fetal distress.

The human placenta produces pregnenolone and progesterone from circulating cholesterol. Pregnenolone is converted in the fetal adrenal gland into dehydroepiandrosterone (DHEA), a C19 steroid, then subsequently sulfonated to dehydroepiandrosterone sulfate (DHEAS). DHEAS is converted to 16-OH DHEAS in the fetal liver. The placenta converts 16-OH DHEAS to estriol, and is the predominant site of estriol synthesis.

Estriol can be measured in maternal blood or urine and can be used as a marker of fetal health and wellbeing. DHEA-S is produced by the adrenal cortex of the fetus. This is converted to estriol by the fetal liver.

Test results
If levels of unconjugated estriol are abnormally low in a pregnant woman, this may indicate chromosomal or congenital anomalies like Down syndrome, Smith-Lemli-Opitz syndrome, or Edward's syndrome. Low unconjugated estriol is also associated with placental steroid sulfatase deficiency, an X-linked condition that is characterized by ichthyosis (a skin disease which causes dry, fish-like scales on the skin surface), and other unknown problems.
Because many pathological conditions in a pregnant woman can cause deviations in estriol levels, these screenings are often seen as less definitive of fetal-placental health than non-stress testing. Conditions which can create false positives and false negatives in estriol testing for fetal distress include preeclampsia, anemia and impaired kidney function.

Also you should know
Prenatal Risk Profile is a set of blood tests that measures the levels of several different biochemicals in the mother's blood or serum. They usually include four biochemicals: maternal serum alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), a hormone produced in the placenta; inhibin A (DIA), another hormone; and unconjugated estriol-an estrogen produced by both the fetus and the placenta (uE3). Among these individual biochemicals, a test for maternal serum alpha-fetoprotein (MSAFP), can sometimes be done separately or alone to screen for neural tube defects.

It is important to remember that the Estriol test (as a part of triple or quad screen) is a screening test and not a diagnostic test. This test only notes that a mother is at risk of carrying a baby with a genetic disease. Many women who experience an abnormal test result go on to deliver healthy babies.

Abnormal test results warrant additional testing in order to make a diagnosis. A more conservative approach involves performing a second quad screen followed by a high definition ultrasound. If the testing still maintains abnormal results, a more invasive procedure such as amniocentesis may be performed.

Any invasive procedure should be discussed thoroughly with your healthcare provider and between you and your partner. Additional counseling and discussions with a counselor, social worker or minister may prove helpful.

All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.