Dependence of maternal serum [AFP]/[hCG] median ratios on age of gestation: comparison of trisomy 21 to euploid pregnancies.
BACKGROUND
Current risk calculations for trisomy 21, which are based on multiples of median (MoM), do not take into account possible differences between euploid and trisomy 21 pregnancies that may develop with gestational age. In order to optimize the predictive value of screening tests, we calculated the ratio between maternal serum concentration of alpha-fetoprotein (AFP) and that of human chorionic gonadotropin (hCG) in euploid and in trisomy 21 pregnancies.


METHODS
The medians of the concentration ratios, [AFP]/[hCG] at 16-21 weeks of gestation, were plotted as a function of gestational age for 307 cases of trisomy 21 and were compared with the medians of 30 549 normal karyotype cases.


RESULTS
[AFP]/[hCG] ratio medians were independent of body weight and maternal age. There was a significant difference in the [AFP]/[hCG] ratio when comparing trisomy 21 and euploid pregnancies at each week. This difference became greater with advancing gestational age (P < 0.01).


CONCLUSIONS
There is a significant difference in ratios of [AFP]/[hCG] between euploid and trisomy 21 pregnancies, which may be used to improve detection rates of Down syndrome screening.
Marcus-Braun
N
N
Division of Obstetrics and Gynecology, Soroka University Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. naamamb@bgu.ac.il
Birk
O
O
Manor
E
E
Segal
D
D
Harari
G
G
Toma
I
I
Shalev
S
S
Borochowitz
Z U
ZU
Yaron
Y
Y
Sharony
R
R
Itzhaky
D
D
Shtoyerman
R
R
Appelman
Z
Z
Braun
G
G
D000328:Adult; D006063:Chorionic Gonadotropin / Q000032:analysis / Q000097:blood*; D004314:Down Syndrome / Q000097:blood* / Q000175:diagnosis; D005260:Female; D005865:Gestational Age; D006801:Humans; D009035:Mothers; D011003:Ploidies; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D000509:alpha-Fetoproteins / Q000032:analysis*
D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins