Maternal weight and ethnic adjustment within a first-trimester Down syndrome and trisomy 18 screening program.
OBJECTIVE
To estimate weight and ethnic group correction factors for first-trimester screening markers.


METHODS
Ethnic-specific median MoM free beta hCG and pregnancy associated plasma protein A (PAPP-A) and delta nuchal translucency values were calculated for cohorts of maternal weight (20 lb each) using data from 51,206 patients undergoing first-trimester screening. False-positive rates for Down syndrome and trisomy 18 were evaluated both prior to and after weight and ethnicity adjustment.


RESULTS
Free beta hCG and PAPP-A significantly decreased with increasing maternal weight while nuchal translucency increased by a clinically insignificant amount. For free beta hCG the regression formula indicated that after accounting for maternal weight MoM values were 16% higher for African Americans, 6% higher for Asians and 9% lower for Hispanics compared to Caucasians (p < 0.001, p = 0.001, p < 0.001, respectively) but there was no significant difference for Asian Indians. For PAPP-A, MoM values were 35% higher for African Americans (p < 0.001) but were not significantly different for the other ethnic groups compared to Caucasians. Down syndrome false-positive rates did not vary with maternal weight prior to (p = 0.291) or after weight adjustment of biochemistry (p = 0.054). Trisomy 18 false-positive rates varied significantly with weight both before (OR = 1.455 per 20-pound increase, p < 0.001) and after (OR = 1.066 per 20-pound increase, p = 0.01) weight adjustment of biochemistry; however, the odds ratio was greatly reduced after weight adjustment.


CONCLUSIONS
The first-trimester screening markers, free beta hCG, PAPP-A and nuchal translucency vary with maternal weight and ethnicity. Adjustment of free beta hCG and PAPP-A is indicated but adjustment of nuchal translucency results may not be necessary.
Krantz
David A
DA
Research Division, NTD Laboratories, Huntington Station, New York 11746, USA. dakrantz@ntdlabs.com
Hallahan
Terrence W
TW
Macri
V James
VJ
Macri
James N
JN
D001835:Body Weight; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D002887:Chromosomes, Human, Pair 18 / Q000235:genetics; D015331:Cohort Studies; D004314:Down Syndrome / Q000175:diagnosis* / Q000208:ethnology* / Q000235:genetics; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008403:Mass Screening; D048208:Nuchal Translucency Measurement / Q000592:standards; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011295:Prenatal Care / Q000592:standards; D011296:Prenatal Diagnosis; D044469:Racial Groups; D014314:Trisomy / Q000175:diagnosis* / Q000235:genetics
D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A