The placenta of a normal pregnancy secretes small amounts of a variety of biomarkers such as alpha-fetoprotein (AFP), human chorionic gonadotropin, unconjugated estriol
, inhibin A, pregnancy-associated placental protein A (PAPP-A), soluble fms-like tyrosine kinase, and placental growth factor.
When alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), and unconjugated estriol
(uE3) are measured together, it's called a triple screen; when inhibin A is added, it's called a quad screen.
On the basis of the manufacturers' literature (IMMULITE 2000 Unconjugated Estriol
(UEs) transforms in the mother's liver to sulfate and glucuronide and is repelled by urine with a half life of 20 to 30 minutes.
8,9) Currently, the best second-trimester test is the quadruple test (AFP, unconjugated estriol
, hCG [total or free [beta]-hCG], and inhibin-A) with an 80% detection rate at a 5% false-positive rate.
5 This association was expanded in the late 1980s, when elevated levels of human chorionic gonadotropin (hCG) and decreased levels of unconjugated estriol
were also reported in DS fetuses.
Levels of four serum markers - inhibin A, MSAFP, HCG, and unconjugated estriol
(uE3) - were analyzed alone and in selected combinations for their association with stillbirth.
For example, microparticle enzyme immunoassay has errors in estradiol measurements due to interference from unconjugated estriol
Patients in the highest risk group (greater than 1:30 risk in this study) undergo CVS, those in the lowest risk group (less than 1:1,500 risk) receive no further testing, and those in the borderline risk group (between 1:30 and 1:1,500 risk) undergo quad screening (serum alpha fetoprotein, hCG, unconjugated estriol
, and inhibin A) in the second trimester and receive a final risk assessment based on all the measures, with a risk cutoff for further testing of 1:270, Dr.
The results of swab tests, urinalysis and other procedures are analyzed to measure a veritable alphabet soup of medical conditions: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol
Study design and validity The proposed integrated test uses measurements of plasma protein A and nuchal translucency in the first trimester, and serum [Alpha]-fetoprotein, unconjugated estriol
, HCG, and inhibin A in the second trimester.
An English study found that measuring human chorionic gonadotrophin was a much better test for detecting the presence of Down's syndrome than methods currently used -- measuring unconjugated estriol
and alpha fetoprotein.