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Maternal age- and gestation-specific risk for trisomy 21
R J Snijders1, K Sundberg, W Holzgreve
1Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, London, UK.
Summary
The risk of trisomy 21 increases with maternal age but decreases with gestational age. Early pregnancy screening for trisomy 21 is crucial for accurate risk assessment.
Area of Science:
- Prenatal diagnostics
- Genetics
- Obstetrics
Background:
- Trisomy 21 (Down syndrome) is a common chromosomal abnormality.
- Accurate risk assessment for trisomy 21 is vital in prenatal care.
- Existing risk models often do not fully account for gestational age.
Purpose of the Study:
- To estimate the risks associated with trisomy 21 based on maternal age and gestational age.
- To develop a predictive model for trisomy 21 prevalence during early pregnancy.
Main Methods:
- Analysis of fetal karyotyping data from 57,614 pregnancies with maternal age ≥35 years.
- Calculation of observed vs. expected trisomy 21 cases across gestational age subgroups (9-16 weeks).
- Regression analysis to derive a smoothed risk curve and formula.
Main Results:
- A formula was derived to estimate trisomy 21 risk by maternal and gestational age.
- Prevalence of trisomy 21 at 12 and 16 weeks gestation was 30% and 21% higher than at 40 weeks, respectively.
- In a separate cohort of 96,127 pregnancies, the model accurately predicted 329 cases (observed 326).
Conclusions:
- Trisomy 21 risk is significantly influenced by both maternal age and gestational age.
- The prevalence of trisomy 21 is higher in early gestation compared to term.
- This study provides a refined tool for early trisomy 21 risk assessment in pregnancy.