Screening For Down Syndrome In The Second Trimester Using Dried Blood Spots

Objective1. To investigate the feasibility and clinical values of dried bloods spots (DBS) as a screening method for detecting Down syndrome (DS).2. To compare the precision and correlation of the two prenatal screening programs--DBS and serum.3. To obtain median values for all screening parameters of each gestational week and to calculate the risk by lifecycle software.Materials and Methods1. The serum samples and DBS of 5002 gravidas were collected from the obstetric clinics of Haidian Women and Children hospital, from May 13th,2009 to October 31 st,2009. Clinical information was collected simultaneously.2. AFP, free P-HCG concentrations were measured for all the serum and DBS samples. UE3 concentrations were measured in all the serum and 1032 DBS samples.3. The median values of three markers in different gestational weeks were obtained from all the patients. Risk ratios of DS, trisomy 18 and open neutral tube defects (ONTD) were obtained according to two markers and three markers by lifecycle software respectively.4. Correlation of all parameters between DBS and serum were compared.5. Pregnancy outcome was followed.6. The detection rates of DBS and serum prenatal screening program were compared, and their correlation was evaluated.Results1. Ages, gestational weeks and weights of the gravidas were in a normal distribution.2. Multiples of medians of AFP, freeβ-HCG and uE3 distribution were described as unimodal curves with their medians and modes close to 1.3. Follow-up rate was 71.27% (3565/5002). There were 457 gravidas with high risks of which 138 accepted amniocentesis. Four patients were diagnosed as DS,4 patients as ONTD and none as trisomy 18 among these 3565 gravidas.4. The positive rate, detective rate (DR) and false positive rate(FPR) of double test with DBS were 3.88%,75% and 3.82% respectively in DS screening, and in ONTD screening the rates were 4.8%,25% and 0.46% respectively.5. In triple test with DBS the positive rate, DR and FPR were 6.78%,50% and 6.71% respectively for DS screening. The detective rate of triple test with DBS was 0 both in trisomy 18 and ONTD screenings.6. The performance of DBS screening program was consistent with that of the serum screening program.7. If the estimated spontaneous loss were concerned, the detective rate of double test in DBS would decrease from 75% to 69.79% at a false positive rate of 3.82%.Conclusions1. The levels of AFP, free p-HCG and uE3 had statistical correlations between DBS and serum specimens.2. The performance of DBS screening program was consistent with that of the conventional serum screening program.3. The screening program with DBS was feasible.4. The detective rate of triple test was no better than double test because of the instability of uE3.5. The DBS screening program is a good prenatal screening program that is especially suitable for the countryside and remote areas with its advantages of good price, preservation and transportation.