Predictive significance of risk value in prenatal screening for fetal trisomy 18

Objective To investigate the clinical application of prenatal screening and diagnosis for trisomy 18.Methods The concentrations of alpha-fetoprotein(AFP) and free beta-human chorionic gonadotropin(hCGβ) in serum of pregnant women were detected by time-resolved fluoroimmunoassay.The risk rate of fetal trisomy 18 with maternal age,weight and biochemical indicators was calculated.The prenatal diagnosis was carried out by traditional amniotic fluid cell culture karyotype analysis.Results 145 658 pregnant women were enrolled in prenatal screening,and 588 women were detected and showed at high risk for trisomy 18.The positive rate was 0.40%.From 318 pregnant women with high risk for trisomy 18,15 trisomy 18 fetuses were identified,and the positive rate was 4.72%.Screening risk values(n) of trisomy 18 were classified to 7 groups: n≥1/50,1/50n≥1/100,1/100n≥1/150,1/150n≥1/200,1/200n≥1/250,1/250n≥1/300 and 1/300n≥1/350 groups.After grading,the positive rates of 7 groups were 17.10%,4.44%,0.00%,0.00%,0.00%,0.00% and 0.00%,respectively.Trisomy 18 in pregnant women with high risk value and the identified pregnant women were significantly concentrated at n≥1/100.The distribution of pregnant women with high risk value showed average in other n value groups,and the positive rates were all 0.Furthermore,there were 477 low risk and 1 220 without screening advanced age pregnant women accepting prenatal diagnosis voluntarily.Every group found 2 trisomy 18 fetuses.Conclusions Trisomy 18 calculating with age and biochemical indicators can be applied into prenatal risk screening.Trisomy 18 in pregnant women with high risk value and the identified fetuses are significantly concentrated at n≥1/100.These data are helpful for genetic counseling.