Maternal weight and ethnic adjustment within a first-trimester Down syndrome and trisomy 18 screening program

Prenat Diagn. 2005 Aug;25(8):635-40. doi: 10.1002/pd.1188.

Abstract

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.

MeSH terms

  • Body Weight*
  • Chorionic Gonadotropin, beta Subunit, Human / blood
  • Chromosomes, Human, Pair 18* / genetics
  • Cohort Studies
  • Down Syndrome / diagnosis*
  • Down Syndrome / ethnology*
  • Down Syndrome / genetics
  • False Positive Reactions
  • Female
  • Humans
  • Mass Screening*
  • Nuchal Translucency Measurement / standards
  • Pregnancy
  • Pregnancy Trimester, First
  • Pregnancy-Associated Plasma Protein-A / analysis
  • Prenatal Care / standards
  • Prenatal Diagnosis
  • Racial Groups
  • Trisomy / diagnosis*
  • Trisomy / genetics

Substances

  • Chorionic Gonadotropin, beta Subunit, Human
  • Pregnancy-Associated Plasma Protein-A