Purpose of the study: Chromosomal aneuploidies are major causes of perinatal death and childhood handicap. Awareness about screening and prenatal diagnosis for these disorders among obstetricians and primary care physicians is increasing. Since invasive tests like amniocentesis or chorionic villus sampling (CVS) are associated with a risk of miscarriage these tests should be carried out judiciously in pregnancies considered to be at high risk for aneuploidies and other genetic disorders. The purpose of our study was to examine the patterns, trends and outcomes of the various screening procedures and invasive tests results.
Methodology: Retrospective observational study done over a period of 3 years and one month including 433 pregnant women with high risk for genetic disorders undergoing invasive prenatal testing like chorionic villus sampling, amniocentesis or cordocentesis. Data were collected from our department records regarding the maternal age, indication for invasive testing, past obstetric history, family history of genetic syndromes, ultrasound findings in the current sonographic examination and the results of the tests done. Any immediate or late complications of the procedure if any were telephonically addressed.
Results: A total of 436 procedures on 433 patients (418 singleton,12 single fetus of twin, 3 both fetuses of twins) were done out of which 281 were amniocentesis(64.4%), 153 were chorionic villus sampling (35.1%) and 2 were cordocentesis(< 1%). Of the 436 procedures, 373(85.5%) were done for positive screening tests for chromosomal aneuploidies and 63(14.4%) were done for previous history of genetic syndromes. The positive predictive value of biochemical marker alone was around 2.7% and higher around 13% for a combined first trimester or a second-trimester screen along with ultrasound abnormalities. The higher the biochemical risk does not translate into higher chance of chromosomal abnormality. Nineteen percentage of fetuses with NT above 95th centile had chromosomal abnormality. Twenty-one percentage of fetuses with absent nasal bone in our study had trisomy 21.
Conclusion: Aneuploidy screening is the most common indication for prenatal invasive testing with dual marker combined with nuchal translucency, nasal bone, tricuspid regurgitation and ductus venosus flow providing the best detection rates. The chance of an affected fetus in a patient with aneuploidy screen positive overall is only 6.7%.
Keywords: Amniocentesis; Aneuploidy; Chorionic villus sampling; Invasive tests; Prenatal test.
© Federation of Obstetric & Gynecological Societies of India 2021.