Second Trimester Serum Markers
Section snippets
Addition of Inhibin A
Inhibin is a family of alpha-beta subunit glycoproteins named in the 1930s for their ability to selectively inhibit the secretion of the anterior pituitary gonadotropin, follicle stimulating hormone. In 1992, van Lith and coworkers, using an immunoassay that measured all forms of inhibin and its alpha subunit, reported that second trimester maternal serum total inhibin levels tended to be elevated in Down syndrome pregnancy.9 By 1994 through 1996, with the advent of a specific immunoassay that
Reliability of the Inhibin A Assay
The assay currently available to measure inhibin A is in one format, an enzyme-linked immunosorbent assay (ELISA) produced by Diagnostic Systems Laboratories, Inc. (DSL), Webster, TX. The monoclonal antibodies used in the assay (one directed against the alpha-subunit and one against the beta-subunit) were developed by Nigel Groome at Oxford Brookes University, UK. The assay can be performed manually or by using an automated immunoassay platform. The DSL assay has been validated for use in Down
Hyperglycosylated HCG
A more recent research finding of some interest has been the observation that a specific variant of hCG, hyperglycosylated hCG (h-hCG), also called invasive trophoblast antigen (ITA), has potential value as a screening marker for fetal Down syndrome. H-hCG is a variant with an increased carbohydrate content, making it structurally more complex. Rather than having predominantly biantenary (two branches) carbohydrate side chains, h-hCG has a proportion of triantenary (three branched) side chains.
Conclusions
In the United States and Canada, second trimester serum screening is transitioning from the measurement of triple markers to quad markers. Maternal serum inhibin A, measured in the second trimester, is an important clinical marker, and the available assay performs properly. Recent studies on the clinical utility of hyperglycosylated hCG as a second trimester marker have not replicated the impressive results seen in the initial reports. However, maternal urine measurement of h-hCG may improve
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Cited by (37)
Impact of Unconjugated estriol (uE3) assay interference on prenatal screening tests
2022, Clinica Chimica ActaEthical issues in genetic counseling
2017, Best Practice and Research: Clinical Obstetrics and GynaecologyCitation Excerpt :However, new tests that integrate first- and second-trimester markers into a single risk estimate that is reported in the second trimester show major promise and provide the best possible screening performance. For women having this integrated test and for those who present for prenatal care later than the first trimester, the second trimester biomarkers will continue to be an important resource [64]. In decision-making about risk assessment for chromosomal anomalies, clinicians should be guided by transparency about such risk assessment.
Screening for fetal aneuploidy
2016, Seminars in PerinatologyCitation Excerpt :A number of other biochemical markers have also been studied and implemented in aneuploidy screening programs. Unconjugated estriol (uE3),26 human chorionic gonadotropin (hCG),27 and dimeric inhibin A,7,28,29 all add sensitivity and specificity to second trimester biochemical screening for DS and are included in a test routinely referred to as the quad screen.7,30 The second trimester maternal serum quad screen reports risk results for Down syndrome, trisomy 18, and neural tube defects.
Inhibin A in second trimester screening of Down's syndrome
2011, Diagnostico PrenatalPrenatal diagnosis: Noninvasive screening
2011, Ultrasound ClinicsCitation Excerpt :However, combining all 4 analytes together into a single screen provides a detection rate of about 81%, with a screen positive rate of 5%.2,3 In fetuses with Down syndrome, the average MSAFP and UE3 levels are 0.73 and 0.73 MoM, respectively7; the total hCG level is double of that of fetuses without Down syndrome at an average level of 2.06 MoM; and the inhibin A level is increased to 1.77 MoM.2,8 In some second-trimester screening programs, the free β-hCG concentration is used because it seems to have a greater discriminatory value than total hCG levels; the average free β-hCG level is 2.66 MoM in fetuses with Down syndrome, which translates into a slightly higher detection rate.7