At the same time, all patients who had undergone the quadruple test (n=1685) during the same period were included. This encompassed a period of eight years. As this was a retrospective study with no issues related to attrition or loss to follow up a total of 1490 patients who had undergone the triple test were included. Sample size: Taking the prevalence of DS in the general population as approximately 0.1 per cent and the prevalence of DS in high-risk population based on literature 10, and our data of prevalence data of trisomy 21 in patients referred to our centre (the study cohort) as 1:250 with five per cent margin of error and 80 per cent power of the study based on the width of the 95 per cent confidence interval (CI) around an expected OAPR for the triple test, the required sample size for assessment of triple test OAPR was calculated as 1471. In this study OAPR was calculated as the ratio of true screen positive to false screen positive 8, 9. So, it is important that the false-positive rate (FPR)/screen positive rate is kept as low as possible so to minimize the number of women offered invasive procedures which will, in turn, reduce the number of miscarriages of healthy foetuses. If a screening test has a high OAPR, more affected pregnancies will be successfully diagnosed for every miscarriage caused by invasive testing 8. OAPR is the likelihood of a woman having a DS pregnancy confirmed by chorionic villous sampling (CVS) or amniocentesis if her screen risk is high 7. This was a retrospective observational study conducted at Apollo Centre for Fetal Medicine, Indraprastha Apollo Hospital, New Delhi, India between December, 2009 to December, 2017 after attaining the required clearance from the Institutional Ethics and Review board and in accordance with the Helsinki Declaration of 1975, as revised in 2000. diagnosing trisomy 21) given a positive risk of qadruple test compared to the triple test, and to further evaluate the improvement in DRs of quadruple test when it is combined with a genetic sonogram at 18-20 wk of gestation in a tertiary care referral centre in New Delhi. The present study was undertaken to compare the odds of being affected with DS ( i.e. This is the standard investigation in the Western world but is yet to be established in India. serum inhibin A in addition to the triple test) though known to have a higher sensitivity as compared to the triple test is still not being used for screening of aneuploidies in India universally because of a lack of awareness, cost constraints and laboratory availability.įirst trimester combined screening is the main DS screening test with a DR of 93.8 per cent with a 1.9 per cent false positive rate 6. Quadruple test (additional biochemical marker, i.e. In many parts of the country even today, second-trimester maternal serum screening in the form of the triple test [serum alpha foetoprotein, serum total beta-human chorionic gonadotrophin (HCG) and serum unconjugated estriol) is generally being used to screen for foetal aneuploidies. This genetic sonogram, if done in a regular low volume clinic has a detection rate (DR) of 56 per cent for a three per cent false positive rate, whereas if done by dedicated foetal medicine clinics, has a DR of 80 per cent 5. In India, in many of the low resource settings a genetic sonogram done at 18-20 wk gestation is the only screening tool available for the detection of aneuploidies. Although the knowledge about screening for DS is increasing both in the public and private sector, a definitive protocol from professional bodies or the Government is still not available. Published data suggest that, in India, 21,400 children with DS are born every year 2 and the birth prevalence is reported to vary from one in 1361 to one in 692 in various studies 3, 4. Down syndrome (DS) is the most common cause of developmental delay and accounts for 15-30 per cent of individuals with intellectual disabilities 1.
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