Objective: The purpose of this prospective study was to assess the value of maternal serum screening between 11 and 15 weeks of gestation to detect fetal Down syndrome.
Study design: Blood samples were collected on 993 women between 11 and 15 weeks' gestation before amniocentesis. Ninety percent were > or = 35 years old. Samples were coded and assayed for alpha-fetoprotein, unconjugated estriol, and human chorionic gonadotropin. Medians were established at each week between 11 and 15 from 836 normal, singleton pregnancies.
Results: We used a computer-generated cut-off risk for Down syndrome of one in 365 at term; nine of 11 (82%) Down syndrome pregnancies were identified. There were 23% false-positive results in women > or = 35 years old and 6% in those < 35 years.
Conclusion: These results suggest that maternal serum screening between 11 and 15 weeks may provide an acceptable alternative to screening between 16 and 20 weeks.