Estriol levels are part of a normal prenatal screening schedule for birth defect risks. Coupled with measurement of alpha-fetoprotein, or AFP, human chorionic gonadotropin, or hCG, and inhibin-A, it can fairly reliably detect increased risk for birth defects such as Down syndrome. Since estriol is part of a panel of tests, its independent measurement is less informative, and so it is possible to have a healthy child despite aberrations in estriol level.
Significance
Specific birth defects, such as Down syndrome, can cause changes in the protein production of a fetus during pregnancy. During standard prenatal care, estriol is detected as part of a triple or quad screen for the strongest indicators of risk of birth defects. Estriol itself is a hormone that is made in both the placenta and the fetal liver. It circulates freely in the mother's bloodstream, where it can be detected by laboratory tests.
Types
Estriol is one of the key components to the triple or quad screen typically performed between 15 and 20 weeks of pregnancy. These tests measure alpha fetoprotein, estriol, human chorionic gonadotropin and optionally, inhibin-A. Each of these proteins is detected in the maternal bloodstream, and taken together can identify risk of birth defect at a greater accuracy than any of the tests alone.
Considerations
The estriol level, as well as other components of the triple or quad test, can have varying degrees normal levels, because they depend on variable factors. According to Kids Health, a pregnant woman's age, weight, race and whether she has diabetes will all influence each of the measurements of the screen, including estriol level. Additionally, if a woman is carrying more than one fetus at once, the levels of all these proteins will change.
Benefits
The simultaneous measurement of all four of the components to the quad screen can predict Down syndrome in up to 80 percent of cases. This implies that some birth defects will escape detection by estriol levels and similar tests. Alternatively, the false positive rate of these tests is significant, as well. This means that despite an abnormal reading, a child may be developing normally.
Prevention/Solution
An abnormal estriol level, as part of the prenatal screen, only identifies potential risk to the fetus. It does not diagnose a birth defect specifically. Rather, the physician will proceed with a series of follow-up tests after an abnormal screening test. Follow-up procedures may include amniocentesis or high resolution ultrasound. Only after these more specific tests will a physician be able to diagnose a birth defect.
