Unconjugated estriol

The increased risk of trisomy with advanced maternal age motivates more than half of pregnant women in North America to undergo prenatal diagnosis (most commonly, amniocentesis or chorionic villus sampling, discussed in Oiapter 6). Down syndrome can also be screened by assaying maternal serum levels of a-fetoprotein, chorionic gonadotropin, and unconjugated estriol. This so-called triple screen can detect approximately 70% of fetuses with Down syndrome. 

Solid symbols represent positive cases and open symbols, negative. The negative samples had serum unconjugated estriol (uE3) <0.3 multiples of the median, but resulted in normal births without apparent abnormalities. DH 3 dehydroestriol, 3 Estriol, EpialloPD epiallopregnanediol... 

Serum estriol measurements are commonly used as part of the triple or quad maternal screens for Down syndrome-affected fetuses (see Chapter 54). On average, unconjugated estriol is 0.72 times less than normal (median value at 16 weeks 0.30 to 1.50 pg/L) when fetal Down syndrome is present,... 

Diagnostic Products Corp Package insert for Immulite unconjugated estriol kit, Los Angeles Diagnostic Products Corp, 2003. 

Diagnostic Systems Laboratories Package insert for DSL-10-3700-1 Active ultra-sensitive unconjugated estriol EIA kit. Webster, Tex. Diagnostic Systems Laboratories, 2003. 

LMP, Gestation age estimated from last menstrual period US, gestational age estimated from ultrasound measurements AFP, alpha fetoprotein uEi, unconjugated estriol CG, chorionic gonadotropin DIA, dimeric inhibin A. 

Figure 54-7 Computation of median values for maternal serum unconjugated estriol (uEj) in the second trimester.The observed average gestational age from Table 54-4 is plotted on the horizontal axis and the median of that week s uEs measurements on the vertical logarithmic axis.The thin vertical lines represent the 95% confidence intervals of the medians.The line represents the results of a linear regression analysis of log uEs versus age weighted by the square root of the number of samples.The equation of that line in completed weeks is median uEj = jQ0.09i6Sx(weeks)-i.6i8 Corresponding equation for day-specific medians is median uE.-...

Figure 54-10 A comparison of the associations between gestational age and the four second trimester maternal serum markers for Down syndrome. For each of the analytes, the median at 15 weeks gestation has been assigned a value of 100%. Each subsequent median is represented as a percentage of that initial median. The marker that has the weakest association with gestational age is dimeric inhibin A (DIA).The strongest associations are found for unconjugated estriol (uEa) and chorionic gonadotropin (CG).The association between gestational age and alpha fetoprotein (AFP) is intermediate.

Bradley LA, Canick JA, Palomaki GE, Haddow JE. Undetectable maternal serum unconjugated estriol levels in the second trimester risk of perinatal complications associated with placental sulfatase deficiency. Am J Obstet Gynecol 1997 176 531-5. 

Phillips OP, Elias S, Shuhnan LP, Andersen RN, Morgan CD, Simpson JL. Maternal serum screening for fetal Down syndrome in women less than 35 years of age using a-fetoprotein, hCG, and unconjugated estriol a prospective 2-year study. Obstet Gynecol 1992 80 353-8. 

Most of the assays now carried out with isoluminol derivatives are solid-phase competitive assays (Fig. 2), in which the analyte to be determined competes with the labeled analyte for the available binding sites on antibodies that are immobilized on the solid phase. Thus, plastic microspheres have been used to immobilize antibodies for estriol (K12) or thyroxine (W9). Estradiol antibodies have been immobilized onto plastic tubes (K7) or beads (K16). In all of the above cases, the amount of immunoconjugated hormone label is inversely proportional to the amount of free hormone in the analytical sample. Unconjugated labels are removed by decantation or aspiration from the solid phase, and the specific, immunoconjugated labels are measured in a luminometer. This approach has been successfully applied to progesterone analyses in either serum (D6) or saliva (D5). A review of several separation-based assays with isoluminol analogs was presented a few years ago by Kohen et al. (K18). 

---