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Pregnancy
Gestational Age
Ultrasonography, Prenatal
Prenatal Diagnosis
Amniocentesis
Mass Screening
Down's Syndrome
Pregnancy, High-Risk
Fetal Diseases
Second Pregnancy Trimester
Retrospective Studies
Maternal Age
Sensitivity and Specificity
Pregnancy Outcomes
Risk Factors
Biological Markers
Newborn Infant
Estriol
alpha-Fetoproteins
United States
Co-Publications
24
22
20
19
12
5
4
3
2
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