N. Gayathri, K. L. Malarvizhi, S. Padmanaban
BACKGROUND Every pregnant woman desires a healthy child who is free of anomalies. In general population, the overall risk of having a child with a major malformation is 3% to 5%. The ability conferred by the increasing sophistication of ultrasonography and biochemical testing to screen for foetal abnormalities is of growing importance to obstetricians and their patients, as greater proportion of woman delay childbirth. The incidence of significant chromosomal abnormalities and birth defects is 3% out of which 66% constitutes Down’s syndrome. Down’s Syndrome is the cause of 25% of severe mental retardation in children and throughout the world the frequency is about 0.13% of births. In India, the incidence is 1 in 600-700. It is important to screen for Down syndrome because the foetus usually survives with mental and physical disabilities causing mental trauma to the family and society. Hence, prenatal screening becomes important in order to reduce the live birth of Down’s babies. Aim- 1) Detection rate by NT followed by CVS/amniocentesis in screen positive cases 2) The normograms of nuchal translucency in our study population. 3) Follow up with genetic sonogram after NT screening. MATERIALS AND METHODS Study Design- Prospective Study. In this prospective clinical study, 575 pregnant women were recruited between 10-14 weeks of gestation with singleton pregnancy with known dates over a period of 1 year attending the antenatal clinic at the Department of Obstetrics and Gynaecology at St. Philomena’s Hospital, Bangalore. RESULTS Screening by foetal nuchal translucency was performed for all the 575 pregnant women between 10+6-13+6 weeks of gestation after categorizing into low risk and high-risk group. It also includes detailed survey for any anomalies. In this study, majority of women (49.2%) were between 21-25 years of age, 32.3% between 26-30 years, 13.2% between 31-35 years, 0.5% > 35 years, 4.7% ≤20 years. The sensitivity of nuchal translucency for foetal abnormalities on the whole is 66.6%, specificity is 100%, accuracy is 99.6%. The sensitivity of nuchal translucency for aneuploidy alone is 50%, specificity is 100%, accuracy 99.82%. Sensitivity of nuchal translucency in relation to genetic scan is for detecting foetal abnormalities is 20%, specificity is 100%. Sensitivity of foetal nuchal translucency more than 2.5 mm (95th centile) for screening foetal aneuploidy/cardiac defects is 66.6%, specificity –100%. Positive predictive value – 99.8%. Sensitivity of foetal nuchal translucency more than 2.5 mm (95th centile) for screening aneuploidy is 50%, specificity 96.9%, positive predictive value 99.2%. Foetal abnormalities are significantly related to increased NT with accuracy of 99.8% in high risk population. CONCLUSION Measurement of Nuchal translucency is a non-invasive, reliable, early screening tool to determine the foetus at risk for foetal aneuploidies/structural defects/genetic syndromes. For a false positive rate of 5% about 75% of Trisomy 21 can be detected, when maternal serum free β-HCG and PAPP-A at 10-14 weeks of gestation were also taken into account, the detection rate of chromosomal defects increases upto 85-90%, when absent nasal bone is also included with the first trimester nuchal translucency and serum biochemistry detection rate increases to more than 95%.
