Preliminary estimate for the second-trimester maternal serum screening detection rate of the 45,X karyotype using alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin.
OBJECTIVE
To estimate the detection rate for 45,X pregnancies through second-trimester screening using maternal serum alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol.


METHODS
Twenty-two cases of 45,X were ascertained through a cytogenetics database and an additional 51 cases were identified through publications. Serum analyte concentrations were reviewed for cases with fetal hydrops, cystic hygroma alone, and no evidence of edema. Using the statistical characteristics of this sample of affected pregnancies, computer simulations were carried out to determine the proportion of 45,X pregnancies that should be screen-positive for Down syndrome and trisomy 18. The extent to which additional cases of 45,X might be identified using a protocol specifically designed to detect 45,X pregnancies was also estimated.


RESULTS
Approximately 54% of all 45,X pregnancies should be identifiable through screening for Down syndrome and trisomy 18. The detection rate for cases with hydrops and/or cystic hygroma was 60%, and without edema 33%. If offered with screening for Down syndrome and trisomy 18, 45,X screening could identify approximately 7% more of the affected pregnancies with an incremental rise of 0.2% in the false-positive rate.


CONCLUSIONS
A screening algorithm for 45,X could be developed. However, the number of additional affected pregnancies identified would appear to be too small to justify this screening.
Division of Human Genetics, Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, Connecticut 06030-6140, USA.
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D000465:Algorithms; D015415:Biomarkers / Q000097:blood*; D006063:Chorionic Gonadotropin / Q000097:blood; D004964:Estriol / Q000097:blood; D005260:Female; D005820:Genetic Testing; D006801:Humans; D007621:Karyotyping; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000097:blood; D025064:Sex Chromosome Disorders / Q000175:diagnosis*; D000509:alpha-Fetoproteins / Q000032:analysis
D015415:Biomarkers; D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins; D004964:Estriol