Amniocentesis Following Positive First Trimester Combined Screening: A Comparative Study

The birth of a neonate with chromosomal abnormalities, e.g. Down syndrome has very serious problems for family, society, and for the neonate itself, and therefore prenatal evaluation is imperative in determining the fate of the fetus. This research aimed to assess the association and accuracy of amniocentesis with first-trimester combined screening. In this study, specimens from 1066 cases were analyzed for free Beta human chorionic gonadotropin, pregnancy-associated plasma protein A, along with nuchal translucency and nasal bone ultrasonography from October 2013 till November 2014. Upon observing positive screening, mothers underwent amniocentesis. Finally the amniocentesis results were compared with that of first-trimester screening. Our results determined a direct relation between the high age of the mother and gravidity with P of 0.001 and 0.020 with positive first-trimester screening. Our study attained a 92% accuracy rate of amniocentesis due to one case of mosaicism of trisomy 21, that was not diagnosed, because it was not requested by physician. Only 12 (17.1%) cases out of 70 (mothers with positive first-trimester screening) showed positive amniocentesis, which had a significant relationship with chromosomal abnormality. First trimester combined screening has very high accuracy (94.6%) in prediction of genetic abnormalities. The probability of positive first-trimester screening is directly influenced by number of factors, including the mother age and gravidity. Amniocentesis is necessary for all of mothers with positive first-trimester screening and will almost always detect chromosomal abnormalities.