Fruit of the Womb
Fruit of the Womb

Ethnic Differences in Components of First Trimester Screening for Aneupolidy

In our last post, we briefly discussed the use of fetal nasal bone (NB) assessment in first trimester screening for aneuploidy and mentioned in passing that ethnic differences have been described. The reader below was curious to find out if ethnicity plays a role in the interpretation of the various components of the screening...

• At Wed Jul 02, 11:35:00 PM 2008, Anonymous said…

Out of curiosity, when you mention race being one of the factors taken into consideration, how does that play out? Are you (when combined with the other factors) at a higher risk for an abnormality if you are African American or Asian than you are if you're Caucasian, etc? Thanks.

• At Thu Jul 03, 02:46:00 PM 2008, Kenneth F. Trofatter, Jr., MD, PhD said…

To anonymous July 2: Ethnicity alone does not necessarily increase risk for certain fetal abnormalities or chromosomal abnormalities, but it does factor in to what is considered 'normal' ranges for the maternal serum markers (?-hCG and PAPP-A) in first trimester. Below is an abstract from an article that makes this point. Furthermore, there are differences in the rate of visualization of fetal nasal bones in first trimester in mothers of different ethnic origins. Yeung Leung and colleagues (Am J Obstet Gynecol 2008;epub ahead of print) found a higher incidence of absent nasal bones in women of Asian origin than in Caucasians and, similarly, Prefumo and colleagues (BJOG 2004;111:109-112) found a lower rate of visualization in women of African origin. Thus, when nasal bone detection is included in first trimester risk assessment, its absence may result in greater false positive screening rates in women of these ethnic backgrounds unless that factor is corrected for statistically or by a sufficient ethnic-specific population database.


Maternal weight and ethnic adjustment within a first-trimester Down syndrome and trisomy 18 screening program. Krantz, et al., Prenat Diagn 2005;25:635-40.

OBJECTIVE(S): 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. CONCLUSION(S): 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. Copyright 2005 John Wiley & Sons, Ltd.
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