First Trimester Screening Tests [İlk Trimestre Tarama Testleri]

Screening for chromosomal anomalies in pregnancy is widely practiced throughout the world. Screening for trisomy 21, often in conjunction with screening for neural tube defects, by measuring second trimester maternal serum biochemical markers, has become an established part of obstetric practice in many countries. Although trisomy 21 screening protocols vary between different centers, the average detection rate in prospective studies has been 64 % (range 48-75 %) for a false positive rate of about 5 %. During the last decade, extensive research has demonstrated that effective screening in the first trimester of pregnancy for chromosomal abnormalities can be achieved by assessing levels of maternal serum free b-hCG and pregnancy associated plasma protein-A (PAPP-A) and the ultrasonographic measurement of fetal nuchal translucency. Screening by fetal nuchal translucency reaches a detection rate of about 73 % for trisomy 21 with a 5 % false positive rate. Subsequently, it is estimated that a combination of fetal nuchal translucency with maternal serum free B-hCG and PAPP-A would increase the detection rate to about 90 % for trisomy 21 and also allow the detection of 90 % of other chromosomal abnormalities, including trisomy 13, trisomy 18, Turner syndrome and triploidy. The advent of rapid immunoassay tests has enabled the development of multidisciplinary techniques to replace invasive prenatal diagnostic methods and their inherent risks to the mother and the fetus with noninvasive alternatives. The isolation of fetal cells and DNA from the maternal circulation represents a promising noninvasive approach to prenatal diagnosis. Advances in molecular biology have provided new and sensitive tools for detecting and confirming the existence of fetal cells. However, because of the inconsistent number of fetal cells found in maternal circulation, these techniques have not yet entered routine clinical practice. In this manuscript, we have reviewed and discussed the developments in first trimester screening and noninvasive prenatal diagnostic techniques