Current methods of prenatal screening for Down syndrome and other fetal abnormalities

Prenatal diagnosis of Down syndrome is widely available, but the determination of which patients should undergo prenatal diagnosis is changing. With the recent acceptance of first-trimester and integrated screening as a part of routine clinical practice, there are now a variety of accepted screening protocols for Down syndrome and other aneuploidies. These choices can be confusing both to both patients and providers. The following discussion is meant to outline the various options in prenatal screening, and their individual advantages and disadvantages.     

Use of red blood cells older than five days for neonatal transfusion

Sick neonates often require periodic small volume transfusions (10 mL/kg) to replace blood drawn for laboratory monitoring during their hospital stay. We use red blood cells (RBCs), stored as CPDA-1 whole blood, up to their expiration date, and are unaware of any clinical problems with this practice. We proceeded to confirm our clinical impression by reviewing the hospital records of 22 transfused neonates who received a median of 2.5 RBC transfusions (range 1 to 11) with a volume of 16 mL (range 5 to 38) each, and total volume of 60 mL (range 16 to 152). The RBCs were stored a median of 7 days (range 2 to 27). Following transfusion, there was an increase (P less than .05) in hemoglobin (mean 2.8 +/- 1.6 gm/dL [SD]) and hematocrit (9.0% +/- 4.7%). The bilirubin also rose (0.6 +/- 1.5 mg/dL, P less than .05), but this was not considered clinically significant. No significant change occurred in pH or bicarbonate. Paradoxically, RBCs over 10 days of age resulted in a fall in potassium (-0.9 +/- 0.8 mEq/L, P less than .01), but not below 3.4 mEq/L. We could find no evidence by clinical observation or laboratory indexes that small volume transfusion of RBCs more than 5 days old was deleterious to the newborns studied. By using RBCs up to their expiration date, the number of donor exposures and the potential risk of transfusion-transmitted diseases can be decreased.     

Detecting fetal DNA from dried maternal blood spots: another step towards broad scale non-invasive prenatal genetic screening and feasible testing

Both intact fetal cells and cell-free fetal DNA are present in the maternal circulation and have been used for non-invasive prenatal genetic diagnosis. However, broad clinical application awaits development of robust methods for collecting, transporting and enriching maternal blood samples to recover rare fetal cells. To circumvent this impediment, we have devised a reliable method of fetal DNA detection using dried maternal blood spots and real-time polymerase chain reaction. Fetal Y-specific (DYS1) sequences were detected in all 19 (100%) maternal blood specimens from women carrying male fetuses, in genome equivalents of 4.20-24.68 per ml of blood; the ubiquitous glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene, reflecting both maternal and fetal DNA, concurrently showed 43,684 to 680,357 genome equivalents per ml of blood. The results demonstrate that fetal DNA detection using dried maternal blood spots is highly feasible and easily adaptable for population screening.     

An outcomes analysis of five prenatal screening strategies for trisomy 21 in women younger than 35 years

OBJECTIVE: This study was undertaken to examine the cost-effectiveness and procedural-related losses associated with 5 prenatal screening strategies for fetal aneuploidy in women under 35 years old. STUDY DESIGN: Five prenatal screening strategies were compared in a decision analysis model: triple screen: maternal age and midtrimester serum alpha-fetoprotein, human chorionic gonadotropin (hCG), and unconjugated estriol; quad screen: triple screen plus serum dimeric inhibin A; first-trimester screen: maternal age, serum pregnancy-associated plasma protein A and free beta-hCG and fetal nuchal translucency at 10 to 14 weeks' gestation; integrated screen: first-trimester screen plus quad screen, but first-trimester results are withheld until the quad screen is completed when a composite result is provided; sequential screen: first-trimester screen plus quad screen, but the first-trimester screen results are provided immediately and prenatal diagnosis offered if positive; later prenatal diagnosis is available if the quad screen is positive. Model estimates were literature derived, and cost estimates also included local sources. The 5 strategies were compared for cost, the numbers of Down syndrome fetuses detected and live births averted, and the number of procedure-related euploid losses. Sensitivity analyses were performed for parameters with imprecise point estimates. RESULTS: In the baseline analysis, sequential screening was the least expensive strategy ($455 million). It detected the most Down syndrome fetuses (n=1213), averted the most Down syndrome live births (n=678), but led to the highest number of procedure-related euploid losses (n=859). The integrated screen had the fewest euploid losses (n=62) and averted the second most Down syndrome live births (n=520). If fewer than 70% of women diagnosed with fetal Down syndrome elect to abort, the quad screen became the least expensive strategy. CONCLUSION: Although sequential screening was the most cost-effective prenatal screening strategy for fetal trisomy 21, it had the highest procedure-related euploid loss rate. The patient's perspective on detection versus fetal safety may help define the optimal screening strategy.     

Principles of first trimester screening in the age of non-invasive prenatal diagnosis: screening for other major defects and pregnancy complications

Purpose

First trimester risk assessment plays a major role in the contemporary pregnancy care. It has evolved significantly since its introduction in the 1990s when it essentially consisted of just the nuchal translucency measurement. Today, it involves the measurement of several biophysical and biochemical markers and can assess the risk for a wide array of major chromosomal and non-chromosomal defects as well as other pregnancy-related complications.

Methods

A search of the Medline and Embase databases was done looking for articles about first trimester screening. We performed a detailed review of the literature to evaluate the screening tests currently available and their respective test performance.

Results

The detailed ultrasound examination results in the detection of about half of major structural defects, determination of a very accurate gestational age, and identification of multiple pregnancies as well as their chorionicity. In addition, risk assessment for preeclampsia and early IUGR can be established at this stage. In case of an increased risk, the daily use of low-dose aspirin can be offered at a point in pregnancy when it still can have a positive impact. Additional screening tests for gestational diabetes and macrosomia are available.

Conclusion

Contemporary first trimester screening is essential to establish an individual risk profile and can be used to tailor the pregnancy care.

     

New frontiers in noninvasive, prenatal screening and diagnosis: fetal DNA circulating in maternal blood

Prenatal diagnosis is aimed to provide reliable clinical information to parents and physician on the risk of having babies affected by inherited anomalies or genetic disorders. Placenta is not a barrier between the pregnant woman and her genetically different fetus, but it is the centre of a complex bidirectional transfer. The discovery of circulating fetal DNA in maternal blood has disclosed new strategies to perform noninvasive testing for prenatal diagnosis, without any harm for the fetus. The possibility to measure rapidly and reproducibly fetal cell-free DNA with noninvasive techniques has warranted many clinical applications: gender detection, diagnosis of fetal aneuploidy such as 13, 18 and 21 trisomies, complications of pregnancy, X-linked diseases, cystic fibrosis, and several others.     

Associations between "early" red blood cell transfusion and severe intraventricular hemorrhage, and between "late" red blood cell transfusion and necrotizing enterocolitis

Transfusion of banked donor erythrocytes can be life saving for small and ill neonates with severe anemia or active hemorrhage. However, risks of transfusions exist and must be weighed against potential benefits each time a transfusion is considered. The present review seeks to bring together the published data supporting 2 newly postulated risks of transfusions among very low-birth-weight neonates. The first is an association between "early" red blood cell transfusions, those administered in the first few days after birth, and the subsequent occurrence of a grade 3 or 4 intraventricular hemorrhage. The second is an association between "late" RBC transfusions and the subsequent occurrence of necrotizing enterocolitis. Much remains to be discovered about the pathogenetic links between transfusion and these adverse outcomes. Moreover, work is needed to clearly establish whether transfusions are causatively associated with these adverse outcomes or are covariables. The purpose of this chapter is to review the associations between transfusion and intraventricular hemorrhage and between transfusions and necrotizing enterocolitis and to use these associations to hypothesize that evidence-based improvements in transfusion practice have the potential to improve neonatal intensive care unit outcomes.     

The attitude of pregnant women to the possibilities for the prenatal screening and diagnosis of Down's syndrome in the 2nd trimester

The aim of the study was to assess pregnant women's attitude and receptivity for second trimester prenatal screening and diagnostic tests for fetal Down syndrome [DS], factors that influence attitude formation, sufficiency of patients' information, advisability of introduction of these tests in routine prenatal care Interviews with 129 pregnant women were conducted after they had received written information concerning prenatal DS screening and diagnostic tests Five questions to the point of the matter as well as 14 related to the personal characteristics of the interviewed were included. Ultrasound screening rt]. accepted by 98.4% serum screening--by 93% and invasive prenatal testing--by 90% of the pregnant women Patients receptivity for serum screening and invasive testing Was influenced by factors like age, past obstetric history educational level, religiosity, attitude towards patient's own health For some of the factors statistically significant relationships were present while for others only some trends were outlined Regarding patients' high receptivity for prenatal DS screening and diagnostic tests the latter can be recommended as an element of the routine prenatal care in our country.     

Derivated fetal haemoglobin as a marker for red cell age in the human fetus reflecting stimulated or impaired red blood cell production

We have determined whether derivated fetal haemoglobin (dHbF, consisting of glycated and acetylated HbF) can be used as a cell age marker for fetal red blood cells (RBCs). Cord blood was obtained between 19 and 39 weeks of gestation from 28 alloimmunised anaemic fetuses (23 RhD+ and 5 Kell) and from 20 non-anaemic fetuses and newborns (controls). Density gradient centrifugation was applied to 36 samples (20 RhD+, 15 controls and 1 Kell) to obtain fractions of increasing cell age. Blood samples were used for measurements of mean cellular volume (MCV), mean cell haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), pyruvate kinase activity (PK) and derivated fetal haemoglobin (dHbF) by cation-exchange HPLC. Reticulocytes were counted only in the whole blood samples. In all density gradient separated RBC fractions, the values for MCV, MCH and PK activity decreased and those of MCHC and dHbF increased with increasing density (equivalent to increasing cell age). The mean density was lower for RBCs of the anaemic RHD group (1.072+/-0.007 g/ml) than for the non-anaemic controls (1.077+/-0.005 g/ml) (p<0.05) The RBC density of the Kell sensitised fetus did not differ from those of the controls. In the control group, the values of the cell age markers in whole blood changed significantly with the gestational age, showing an increase of mean age of the erythrocyte population. The best linear relationship was found for dHbF (y=6.28+0.17*weeks; r=0.84; p<0.001). In the anaemic RhD+ fetuses, the RBC age markers did not change with gestational age; the dHbF percentages were lower, and the MCV, MCH, PK values and the reticulocyte counts were higher than in the controls (0.05相似文献   

Comparison of the umbilical artery blood gas, nucleated red blood cell, C-reactive protein, and white blood cell differential counts between neonates of diabetic and nondiabetic mothers

ObjectiveThe aim of this study was to compare the neonatal umbilical artery blood gas values, C-reactive protein (CRP) levels, nucleated red blood cells (NRBCs), and white blood cells (WBCs) differential counts between offspring’s of the diabetic mothers who needed insulin during pregnancy and normal mothers after cesarean delivery.Materials and MethodsA prospective study was performed involving 68 pregnant diabetic women who needed insulin during pregnancy and 410 healthy pregnant women and their neonates with gestational ages between 35 weeks and 41 weeks. Arterial blood was analyzed for pH and blood gas values and venous blood was analyzed for CRP level, NRBC, and WBC differential counts.ResultsThe mean NRBC count in the neonates of diabetic mothers and healthy mothers was 560 ± 985/μL and 202 ± 281/μL, respectively (p < 0.001). The umbilical arterial blood gas showed a lower pH (7.22 ± 0.07 vs. 7.24 ± 0.04, p = 0.004) and a higher pCO₂ (49.33 ± 10.08 vs. 47 ± 8.67, p = 0.045) in neonates of diabetic mothers compared with the controls. Values of pO₂, HCO₃^?, base excess, WBC differential counts, and CRP levels were almost similar in the two groups.ConclusionLower pH, higher pCO₂, and elevated NRBC counts were found in the neonates of diabetic mothers that may be suggestive of chronic intrauterine acidosis.     

Intrauterine intravascular transfusions for severe red blood cell isoimmunization: ultrasound-guided percutaneous approach

Eight pregnancies with severe red blood cell isoimmunization were managed with use of an intravascular approach for intrauterine transfusions. Fetoscopy was not employed, and the procedures were performed percutaneously under direct ultrasound visualization. A total of 16 of 18 attempted transfusions were successfully performed, with four fetuses requiring more than one transfusion. Technical aspects of the procedure as well as its indications, advantages, and drawbacks are discussed.     

Flow cytometric measurement of cell components other than DNA: virtues, limitations, and applications in gynecologic oncology.

Flow cytometry is a high-precision technique for rapid analysis and sorting of cells and particles. In theory, it can be used to measure any cell constituent, provided that a fluorescent tracer is available that reacts specifically and stoichiometrically with that constituent. The technique provides statistical accuracy, reproducibility, and sensitivity and allows simultaneous measurement of several constituents on a cell-to-cell basis. The main drawback of flow cytometry is the lack of visual control and structural information in solid tissues. Careful sample preparation, quality control of all staining and instrumentation procedures, and the use of immunohistologic or cytologic controls are essential for high-quality flow cytometric analysis. The technique has been used successfully for simultaneous measurement of DNA and tumor-associated antigens, oncogene products, proliferation markers, and markers for multidrug resistance in cultured cell lines and in cell suspensions prepared from solid tumors and cervical smears. Flow cytometry has the potential to play an important role in the study of carcinogenesis. With an appropriate panel of monoclonal antibodies, the technique can be used for screening, "biochemical" diagnosis of neoplasia, and rapid drug, hormone, and radiotherapy sensitivity tests.