Analyzing indications of amniocentesis and positive predictive value (PPV) of cytogenetic findings of chromosomal abnormalities

Resumen

nalysis of the causes and extent ofinitial diagnosis by invasive methodof amniocentesis is very important inorder to investigate the chromosomal abnormalities andother severe congenital defects to provide genetic counselingof pregnant women. In Ardebil province (northwestof Iran), due to failures such as infertility, repeated abortionand embryonic anomalies, a study was conducted toanalyze amniotic fluid samples of pregnant mothers, todetermine amniocentesis indications, to determine thefrequency and types of chromosomal abnormalities andadaptability of indication of amniocentesis in pregnantwomen. This retrospective descriptive-analytic study wasconducted on all amniocentesis files (715 referrals to theonly Amniocentesis Center of Ardebil province) over 2years. Data were collected by examining the patients’ file.The variables included: maternal age, indication of amniocentesis,chromosomal anomalies, and type of chromosomalabnormalities. After completing the data, the datawere analyzed using descriptive and analytical statistics inSPSS software version 16. Data analysis showed that themost common cause of amniocentesis was a positive resultin maternal serum screening (58.04%). Chromosomalabnormalities were observed in 5.5%. 56.4% of chromosomalabnormalities were the type of change in number(including trisomy 21) and 35.9% were the structural type.The inversion of chromosome No 9 was 33.3%. Amongpregnant women, 78.7% had 1 indication, 20.6% had2 indications, and 0.7% had 3 or 4 indications. The correlationbetween the results of amniotic fluid karyotypetests and serum tests was significant. The positive predictivevalue analysis showed that the more the numberof indications is more; the positive predictive value tendsto be maximized. Investigating indications and results ofembryonic amniocentesis samples in the present study indicatesthe importance of genetic screening for the identificationof chromosomal abnormalities in 5.5% of pregnantwomen. The most common indication and the mainchromosomal abnormalities detected with amniocentesisin our region are from positive result in maternal serumscreening and trisomy 21, which is consistent with thelatest findings in this area in other countries, respectively.The degree of adaptability of initial indication and theresults of the amniocentesis genetic tests indicated thatserum tests have undertaken a major contribution fromthe results for amniocentesis. In the analysis of indications,if the differentiation threshold regulated for invasivediagnostic tests is considered higher, probability ofdrift and the birth of babies with chromosomal defectswill decrease.