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Down syndrome, also known as Trisomy 21 (Down's syndrome, DS), is the most common chromosomal disorder in newborns, the rate was 1.3 ‰ live births. Not more, brought unusually heavy burden to society, the family, the majority of pregnant women prenatal screening for fetal Down syndrome, to identify high-risk populations, for prenatal diagnosis, the detection of Down's children therapeutic abortion, an important measure to reduce the rate of birth defects, and improve the quality of the population. Of the more commonly used program for maternal serum alpha-fetoprotein (alpha fetoprotein, AFP) and free beta human chorionic gonadotropin (human chorionic gonadotropin, HCG) is 35 years of age, pregnant women at 15-20 weeks of gestation period two associated screening. According to regional reports, the two joint screening the general detection rate (detection rate, DR) 66.7-75% positive rate for high-risk pregnant women may account for 5.8-8% of the population of the entire screening, and this part of the high-risk groups fetal karyotype analysis found that less than 1% of real Down's children, it is necessary to improve the screening efficiency. Objective: to investigate the region gestational age with Down screening populations age, weight, gestational inferior distribution. 2. Contemplated in the existing second trimester the bivalent screening system based on large sample survey, around two evaluation prenatal screening efficiency of the detection rate and false positive rate of Down's children an important indicator of gestational age and production before the screening efficiency analysis of the relationship to the discovery of the higher efficiency of the region, screening for gestational age or gestational age segment. Economic evaluation, to assess whether the economic benefits of different gestational age screening to find the region's high economic returns gestational age calculated by the cost-effectiveness and cost-effectiveness. Subjects and methods: 1. Objects: in the second trimester (15-20 weeks gestation) collected between May 1, 2005 to 31 December 2008 in Shaoxing City, MCH serological screening and Maternal and Child Health Hospital, Shaoxing City singleton pregnancy or childbirth and labor induction of Shaoxing City, Maternal and Child Health the network belongs health institutions to investigate. All survey content from the medical record, prenatal screening records, prenatal diagnostic records. 2. Estimate gestational age: menstrual rules and can remember the last menstrual gestational age based on last menstrual projections, irregular menstrual periods or can not remember the last menstrual period ultrasound to estimate gestational age (<14 weeks measuring head and hip diameter ≥ 14 weeks measuring biparietal diameter). 3. Drawn and check the indicators: pregnant 15-20 weeks to extract 2ml venous serum was separated, set -20 ℃ refrigerator detection within a week, the detection of the second trimester maternal serum AFP and free β-HCG levels. Amniocentesis at 16-22 weeks of gestation, the amniotic fluid taken 20 ml of; cordocentesis at 21-39 weeks of gestation, umbilical cord blood, samples taken from 2 ml of; appearance of suspicious the neonatal extracted peripheral blood 2 ml of cell culture, karyotype analysis. 4. Reagents and instruments: time-resolved immunofluorescence assay (DELFIA, Wallac), reagents and apparatus were obtained from Perkin Elmer, USA Products, Reagents dual labeling kit (AFP / free β-HCG) instrument VICTOR TM 1420 multi-labeled immunoassay system. Data processing using the the Wallac provided Multicalc prenatal screening software processing. The chromosome analysis Beijing Guolian Online chromosome analyzer. Grouping: screening efficiency to compare different gestational age, pregnant women included in the study are grouped according to gestational age, 15 weeks of gestation (15 weeks -15 weeks 6 ), 16 gestational age group (the 16 weeks -16 weeks the 6 ), 17 weeks of gestation group (17 weeks -17 weeks 6 ), 18 weeks of gestation group (18 weeks -18 weeks < sup> 6 ), 19 weeks of gestation group (19 weeks -19 weeks 6 ) and 20 weeks of gestation group (20 weeks -20 weeks the 6 ), a total of 6 groups. Gestational age estimates may exist certain errors, but also for the convenience of clinical operations in the actual operation, the merger again a few weeks of gestation as a group to gestational age segment packet analysis, respectively for 15-18 6 < gestational age ,16-18 6 / sup> gestational age ,15-20 6 gestational age. Results judge: risk ≥ 1/270, is the rate of Down high risk. 7 results calculated: (1) the detection rate of Down's children (DR%) = high-risk screening / diagnosis of Down's number and the number of diagnosed with Down; (2) screening false positive rate (false-positive rate, FPR %) = (number of screening high-risk - screening high-risk and diagnosed with Down's number) / screening number. (3) economics evaluation of cost-effectiveness = diagnosed with Down's child required cost / cost-effectiveness of the number of cases of Down's children diagnosed = diagnosed with Down's child benefits / diagnosis of Down's children costs of 8. Statistics analysis: SPSS13.0 software package for statistical analysis, statistical analysis of variance, chi-square test, the fish's exact method. Results: 1. The region screening age, body weight showed a normal distribution, different gestational age screening population age structure statistically significant, F = 0.247, P = 0.781; pregnancies form and there is no significant difference, χ 2 = 11.212, P = 0.737; weight constituting differences with increasing gestational age, weight increase, the difference caused by the gestational age. 2 weeks of gestation and the detection rate of Down's children's correlation. 15 weeks of gestation detected three cases, two cases were missed, the detection rate of 60%, 16 weeks of gestation detected in six cases, and 17 weeks of gestation detected in 7 cases, 18 weeks of gestation detected three cases, no missed detection rate of 100% . 16, 17 and 18 weeks of gestation combination and the group between 15 and 19 weeks of gestation, no significant difference after the merger with the former, there are differences, p value 0.013 16-18 6 pregnant detection rate compared with other gestational age segment of the peripheral portion, although not statistically significant, but higher than the other weeks of gestation period for 100%. 3. Significant correlation between gestational age with Down's screening false positive rate. Significant differences between gestational age group there were false positive rate, χ 2 = 444.190, P <0.001, the lowest of the 17 and 18 weeks of gestation group. The 16-18 six gestational age segment with gestational age segment (15-18 6 gestational age ,15-20 6 gestational age) compared there is also a significant difference, the χ 2 = 46.826, P <0.01, significantly lower than other gestational age segment. 4. Economic evaluation. The economic burden of disease in cases of Down syndrome patients as a standard, cost-effectiveness and cost-effectiveness of gestational age-related. Group due to no detection of Down's children, the highest costs in the 19th and 20th weeks of gestation; other gestational age groups, the highest of 15 weeks' gestation, for 547,901 yuan; 17 weeks of gestation were the lowest for 383,494 yuan. Cost-effective, and 17 weeks of gestation group, the best cost-effective, 1.18; 19 and 20 weeks of gestation group effective 16-18 6 gestational age segment compared with other gestational age, the lowest cost-effectiveness for 430,373 yuan, the most cost-effective, is 1.06. Conclusion: the region screening age and weight of a normal distribution. Different gestational age weight distribution differences, this difference is caused by the gestational age. The gestational age age, gravidity distribution was no significant difference, excluding the impact of the above factors on the efficiency of screening. Analysis from Down syndrome detection rate and false positive rate, screening the best time period in this gestational age group at 16-18 weeks, screening, detection rate and false positive rate can be reduced missed risk, reduce amniocentesis, cordocentesis traumatic operation and consequential anxiety for pregnant women and their families, and to avoid the waste of medical resources, improve screening effectiveness. Increase screening indicators, do not increase the economic burden and existing computer software can encourage pregnant women prenatal screening at 16-18 weeks of gestation, improve prenatal screening efficiency. The gestational age the exclusion of the age, pregnant inferior impact case, the different efficiency, may be related to the distribution of serum markers exist related to the window period, pending further study. This study shows that the economic benefits generated by the 16 and 18 weeks of gestation, the best is the best screening in addition to gestational age segment. In short, from the study of the region between 16 and 18 weeks of gestation for Down syndrome screening gestational age segment.
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